コミュニティを探したのですが同様の症状が見つからず、質問させていただきます。

当初は問題なく購入まで動作していたのですが、
支払方法を追加したところ、カート画面で「購入する」や支払方法の変更をしようとすると、「購入エラー　購入処理でエラーが発生しました。」の表示が出るようになってしまいました。

新たにec-cubeを別ディレクトリにインストールし、プラグインなしのまっさらなままDBだけ共通の状態で試してみましたが依然同じ症状が発生しております。

ログを確認したのですが、どこで支障が生じているのかわからず、質問させていただく次第です。

ご教授いただければ幸いです。

【システム環境】
EC-CUBE 3.0.16
サーバーOS　Linux
DBサーバー　MySQL 5.6.23-log
WEBサーバー　Apache
PHP　5.4.45
レンタルサーバ　ロリポップ

【状況発生時のログ】
（カートに商品がある状態）カート→ログイン→購入→エラー表示

[2018-10-15 18:15:21,709095] eccube.INFO [0bb7a9e0] [43e0bdf4] [1] [LogListener:logResponse:96] - < 200 [GET, /shop_new/html/cart, 12x.20x.9x.xx, https://www.hogehoge.com/shop_new/html/shopping/shopping_error, Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/69.0.3497.100 Safari/537.36]

[2018-10-15 18:15:21,700746] eccube.INFO [0bb7a9e0] [43e0bdf4] [1] [RouterListener:onKernelRequest:146] - Matched route "block_category". {"route_parameters":{"_controller":"\\Eccube\\Controller\\Block\\CategoryController::index","_route":"block_category"},"request_uri":"https://www.hogehoge.com/shop_new/html/block/category"} [GET, /shop_new/html/cart, 12x.20x.9x.xx, https://www.hogehoge.com/shop_new/html/shopping/shopping_error, Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/69.0.3497.100 Safari/537.36]

[2018-10-15 18:15:21,698800] eccube.INFO [0bb7a9e0] [43e0bdf4] [1] [RouterListener:onKernelRequest:146] - Matched route "block_login". {"route_parameters":{"_controller":"\\Eccube\\Controller\\Block\\LoginController::index","_route":"block_login"},"request_uri":"https://www.hogehoge.com/shop_new/html/block/login"} [GET, /shop_new/html/cart, 12x.20x.9x.xx, https://www.hogehoge.com/shop_new/html/shopping/shopping_error, Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/69.0.3497.100 Safari/537.36]

[2018-10-15 18:15:21,615734] eccube.INFO [0bb7a9e0] [43e0bdf4] [1] [RouterListener:onKernelRequest:146] - Matched route "block_search_product". {"route_parameters":{"_controller":"\\Eccube\\Controller\\Block\\SearchProductController::index","_route":"block_search_product"},"request_uri":"https://www.hogehoge.com/shop_new/html/block/search_product"} [GET, /shop_new/html/cart, 12x.20x.9x.xx, https://www.hogehoge.com/shop_new/html/shopping/shopping_error, Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/69.0.3497.100 Safari/537.36]

[2018-10-15 18:15:21,609707] eccube.INFO [0bb7a9e0] [43e0bdf4] [1] [RouterListener:onKernelRequest:146] - Matched route "block_cart". {"route_parameters":{"_controller":"\\Eccube\\Controller\\Block\\CartController::index","_route":"block_cart"},"request_uri":"https://www.hogehoge.com/shop_new/html/block/cart"} [GET, /shop_new/html/cart, 12x.20x.9x.xx, https://www.hogehoge.com/shop_new/html/shopping/shopping_error, Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/69.0.3497.100 Safari/537.36]

[2018-10-15 18:15:21,423953] eccube.INFO [0bb7a9e0] [43e0bdf4] [1] [LogListener:logRequest:83] - > GET /shop_new/html/cart [GET, /shop_new/html/cart, 12x.20x.9x.xx, https://www.hogehoge.com/shop_new/html/shopping/shopping_error, Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/69.0.3497.100 Safari/537.36]

[2018-10-15 18:15:21,354009] eccube.INFO [NULL] [43e0bdf4] [NULL] [RouterListener:onKernelRequest:146] - Matched route "cart". {"route_parameters":{"_controller":"\\Eccube\\Controller\\CartController::index","_route":"cart"},"request_uri":"https://www.hogehoge.com/shop_new/html/cart"} [GET, /shop_new/html/cart, 12x.20x.9x.xx, https://www.hogehoge.com/shop_new/html/shopping/shopping_error, Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/69.0.3497.100 Safari/537.36]

[2018-10-15 18:15:14,602296] eccube.INFO [0bb7a9e0] [3b15a291] [1] [LogListener:logResponse:96] - < 200 [GET, /shop_new/html/shopping/shopping_error, 12x.20x.9x.xx, https://www.hogehoge.com/shop_new/html/shopping, Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/69.0.3497.100 Safari/537.36]

[2018-10-15 18:15:14,591687] eccube.INFO [0bb7a9e0] [3b15a291] [1] [RouterListener:onKernelRequest:146] - Matched route "block_category". {"route_parameters":{"_controller":"\\Eccube\\Controller\\Block\\CategoryController::index","_route":"block_category"},"request_uri":"https://www.hogehoge.com/shop_new/html/block/category"} [GET, /shop_new/html/shopping/shopping_error, 12x.20x.9x.xx, https://www.hogehoge.com/shop_new/html/shopping, Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/69.0.3497.100 Safari/537.36]

[2018-10-15 18:15:14,588181] eccube.INFO [0bb7a9e0] [3b15a291] [1] [RouterListener:onKernelRequest:146] - Matched route "block_login". {"route_parameters":{"_controller":"\\Eccube\\Controller\\Block\\LoginController::index","_route":"block_login"},"request_uri":"https://www.hogehoge.com/shop_new/html/block/login"} [GET, /shop_new/html/shopping/shopping_error, 12x.20x.9x.xx, https://www.hogehoge.com/shop_new/html/shopping, Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/69.0.3497.100 Safari/537.36]

[2018-10-15 18:15:14,487643] eccube.INFO [0bb7a9e0] [3b15a291] [1] [RouterListener:onKernelRequest:146] - Matched route "block_search_product". {"route_parameters":{"_controller":"\\Eccube\\Controller\\Block\\SearchProductController::index","_route":"block_search_product"},"request_uri":"https://www.hogehoge.com/shop_new/html/block/search_product"} [GET, /shop_new/html/shopping/shopping_error, 12x.20x.9x.xx, https://www.hogehoge.com/shop_new/html/shopping, Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/69.0.3497.100 Safari/537.36]

[2018-10-15 18:15:14,394425] eccube.INFO [0bb7a9e0] [3b15a291] [1] [RouterListener:onKernelRequest:146] - Matched route "block_cart". {"route_parameters":{"_controller":"\\Eccube\\Controller\\Block\\CartController::index","_route":"block_cart"},"request_uri":"https://www.hogehoge.com/shop_new/html/block/cart"} [GET, /shop_new/html/shopping/shopping_error, 12x.20x.9x.xx, https://www.hogehoge.com/shop_new/html/shopping, Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/69.0.3497.100 Safari/537.36]

[2018-10-15 18:15:14,272142] eccube.INFO [0bb7a9e0] [3b15a291] [1] [LogListener:logRequest:83] - > GET /shop_new/html/shopping/shopping_error [GET, /shop_new/html/shopping/shopping_error, 12x.20x.9x.xx, https://www.hogehoge.com/shop_new/html/shopping, Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/69.0.3497.100 Safari/537.36]

[2018-10-15 18:15:14,209168] eccube.INFO [NULL] [3b15a291] [NULL] [RouterListener:onKernelRequest:146] - Matched route "shopping_error". {"route_parameters":{"_controller":"\\Eccube\\Controller\\ShoppingController::shoppingError","_route":"shopping_error"},"request_uri":"https://www.hogehoge.com/shop_new/html/shopping/shopping_error"} [GET, /shop_new/html/shopping/shopping_error, 12x.20x.9x.xx, https://www.hogehoge.com/shop_new/html/shopping, Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/69.0.3497.100 Safari/537.36]

[2018-10-15 18:15:13,626317] eccube.INFO [0bb7a9e0] [1849a8b6] [1] [LogListener:logResponse:94] - < 302 https://www.hogehoge.com/shop_new/html/shopping/shopping_error [POST, /shop_new/html/shopping/confirm, 12x.20x.9x.xx, https://www.hogehoge.com/shop_new/html/shopping, Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/69.0.3497.100 Safari/537.36]

[2018-10-15 18:15:13,478103] eccube.INFO [0bb7a9e0] [1849a8b6] [1] [LogListener:logRequest:83] - > POST /shop_new/html/shopping/confirm [POST, /shop_new/html/shopping/confirm, 12x.20x.9x.xx, https://www.hogehoge.com/shop_new/html/shopping, Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/69.0.3497.100 Safari/537.36]

[2018-10-15 18:15:13,404130] eccube.INFO [NULL] [1849a8b6] [NULL] [RouterListener:onKernelRequest:146] - Matched route "shopping_confirm". {"route_parameters":{"_controller":"\\Eccube\\Controller\\ShoppingController::confirm","_route":"shopping_confirm"},"request_uri":"https://www.hogehoge.com/shop_new/html/shopping/confirm"} [POST, /shop_new/html/shopping/confirm, 12x.20x.9x.xx, https://www.hogehoge.com/shop_new/html/shopping, Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/69.0.3497.100 Safari/537.36]

[2018-10-15 18:15:07,962453] eccube.INFO [0bb7a9e0] [05034461] [1] [LogListener:logResponse:96] - < 200 [GET, /shop_new/html/shopping, 12x.20x.9x.xx, https://www.hogehoge.com/shop_new/html/shopping/login, Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/69.0.3497.100 Safari/537.36]

[2018-10-15 18:15:07,943941] eccube.INFO [0bb7a9e0] [05034461] [1] [RouterListener:onKernelRequest:146] - Matched route "block_category". {"route_parameters":{"_controller":"\\Eccube\\Controller\\Block\\CategoryController::index","_route":"block_category"},"request_uri":"https://www.hogehoge.com/shop_new/html/block/category"} [GET, /shop_new/html/shopping, 12x.20x.9x.xx, https://www.hogehoge.com/shop_new/html/shopping/login, Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/69.0.3497.100 Safari/537.36]

[2018-10-15 18:15:07,940409] eccube.INFO [0bb7a9e0] [05034461] [1] [RouterListener:onKernelRequest:146] - Matched route "block_login". {"route_parameters":{"_controller":"\\Eccube\\Controller\\Block\\LoginController::index","_route":"block_login"},"request_uri":"https://www.hogehoge.com/shop_new/html/block/login"} [GET, /shop_new/html/shopping, 12x.20x.9x.xx, https://www.hogehoge.com/shop_new/html/shopping/login, Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/69.0.3497.100 Safari/537.36]

[2018-10-15 18:15:07,908351] eccube.INFO [0bb7a9e0] [05034461] [1] [RouterListener:onKernelRequest:146] - Matched route "block_search_product". {"route_parameters":{"_controller":"\\Eccube\\Controller\\Block\\SearchProductController::index","_route":"block_search_product"},"request_uri":"https://www.hogehoge.com/shop_new/html/block/search_product"} [GET, /shop_new/html/shopping, 12x.20x.9x.xx, https://www.hogehoge.com/shop_new/html/shopping/login, Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/69.0.3497.100 Safari/537.36]

[2018-10-15 18:15:07,901981] eccube.INFO [0bb7a9e0] [05034461] [1] [RouterListener:onKernelRequest:146] - Matched route "block_cart". {"route_parameters":{"_controller":"\\Eccube\\Controller\\Block\\CartController::index","_route":"block_cart"},"request_uri":"https://www.hogehoge.com/shop_new/html/block/cart"} [GET, /shop_new/html/shopping, 12x.20x.9x.xx, https://www.hogehoge.com/shop_new/html/shopping/login, Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/69.0.3497.100 Safari/537.36]

[2018-10-15 18:15:07,319570] eccube.INFO [0bb7a9e0] [05034461] [1] [LogListener:logRequest:83] - > GET /shop_new/html/shopping [GET, /shop_new/html/shopping, 12x.20x.9x.xx, https://www.hogehoge.com/shop_new/html/shopping/login, Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/69.0.3497.100 Safari/537.36]

[2018-10-15 18:15:07,250391] eccube.INFO [NULL] [05034461] [NULL] [RouterListener:onKernelRequest:146] - Matched route "shopping". {"route_parameters":{"_controller":"\\Eccube\\Controller\\ShoppingController::index","_route":"shopping"},"request_uri":"https://www.hogehoge.com/shop_new/html/shopping"} [GET, /shop_new/html/shopping, 12x.20x.9x.xx, https://www.hogehoge.com/shop_new/html/shopping/login, Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/69.0.3497.100 Safari/537.36]

[2018-10-15 18:15:06,677486] eccube.INFO [0bb7a9e0] [07380d34] [1] [LogListener:logResponse:94] - < 302 https://www.hogehoge.com/shop_new/html/shopping [POST, /shop_new/html/login_check, 12x.20x.9x.xx, https://www.hogehoge.com/shop_new/html/shopping/login, Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/69.0.3497.100 Safari/537.36]

[2018-10-15 18:15:06,671566] eccube.INFO [0bb7a9e0] [07380d34] [NULL] [AbstractAuthenticationListener:onSuccess:216] - User has been authenticated successfully. {"username":"xxxxx@gmail.com";} [POST, /shop_new/html/login_check, 12x.20x.9x.xx, https://www.hogehoge.com/shop_new/html/shopping/login, Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/69.0.3497.100 Safari/537.36]

ご提示いただいたログには、エラーの情報が含まれていないようです。
eccube.ERRORや eccube.WARNING等の記述があれば、そこがエラーのログになります。

支払方法を追加した後、配送業者で支払方法を有効にしていますか？
その辺りの設定も必要だったと思いますので、
再度、管理画面での設定を確認されてみては如何でしょうか？

----------------
株式会社シロハチ
■ECCUBE2系、3系構築カスタマイズご相談ください。
■EC-CUBE3マニュアル
■blog

返信ありがとうございます。

新環境にDBを新たに立てて、環境構築後（この時点では不具合なし）データベースのインポートをして動かすと同じく注文完了時にエラーが出てしまいました。
支払方法、配送方法についても再度確認してみましたが、紐づいての設定に問題はなさそうです。

ログもレベルをDEBUGにして収集してみましtが、やはりERRORやWarningの類は出力されず、エラーがデータベースに起因するようなことはあるのでしょうか？

とりあえず再度環境を構築して、CSVなどで商品データを移行することで今のところは動いていますが、また同じ症状が発生するのではないかと不安な状態です。