UnifiedArchive が見つからないと出ているので、composer のインストールに失敗していると思います
削除して、再インストールしてみてもダメでしょうか？

----------------
EC-CUBEのカスタマイズ、トラブル解決承ります
お気軽にお問い合わせ下さい
https://www.ec-cube.net/integrate/partner/partner.php?partner_id=690

いえ、こちらは、オーナーズストアからインストールしております。今回、オーナーズストア以外からインストールしたプラグインはありません。

他のプラグインで、カラムの構造が変わり、このプラグインに影響したとかそんな感じでしょうかね。

インストールをオーナーズストアからされていないのではないでしょうか？

----------------
EC-CUBEのカスタマイズ、トラブル解決承ります
お気軽にお問い合わせ下さい
https://www.ec-cube.net/integrate/partner/partner.php?partner_id=690

▼テンプレート
[EC-CUBE] 4.0.2
[レンタルサーバ] さくらのVPS
[OS] Centos 7
[PHP] PHP 7.02
[データベース] MySQL 5.5.60-MariaDB
[WEBサーバ] nginx/1.15.8
[ブラウザ] Chrome
[導入プラグインの有無] あれば導入プラグインを記載
[カスタマイズの有無] カスタマイズなし
[現象]

EC Cube 2系から4への移行プラグイン (https://www.ec-cube.net/products/detail.php?product_id=1804)
をインストールし、データのアップロードを試していますが、システムエラーで動作しません。
EC CUBEは、これまでシステムエラーが出やすく、さすがに4はないかなと期待していたのですが。。。

どなたか原因が分かる方はいますでしょうか？
なお、他の無料系のプラグインはすべて入れておりますが、一旦、すべてdisableにしております。

[2019-03-03 21:35:48] app.DEBUG [N/A] [5d43f17] [1] [Eccube\Log\Logger:log:68] - Commit executed. [] [POST, /penguinadmin/data_migration4/config, 131.147.87.32, https://shop.airconshop.jp/penguinadmin/data_migration4/config, Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/72.0.3626.119 Safari/537.36]
[2019-03-03 21:35:48] app.INFO [N/A] [5d43f17] [1] [Eccube\Log\Logger:log:68] - PROCESS END ["data_migration4_admin_config"] [POST, /penguinadmin/data_migration4/config, 131.147.87.32, https://shop.airconshop.jp/penguinadmin/data_migration4/config, Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/72.0.3626.119 Safari/537.36]
[2019-03-03 21:35:48] admin.INFO [uss0ikrloae2dfq9qqemnvutfk] [5d43f17] [1] [Eccube\Log\Logger:log:64] - LOGIC END ["data_migration4_admin_config"] [POST, /penguinadmin/data_migration4/config, 131.147.87.32, https://shop.airconshop.jp/penguinadmin/data_migration4/config, Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/72.0.3626.119 Safari/537.36]
[2019-03-03 21:35:48] admin.ERROR [uss0ikrloae2dfq9qqemnvutfk] [5d43f17] [1] [Eccube\Log\Logger:log:64] - システムエラーが発生しました。 ["Attempted to load class \"UnifiedArchive\" from namespace \"wapmorgan\\UnifiedArchive\".\nDid you forget a \"use\" statement for another namespace?","/home/airconshop_shop/eccube-4.0.1/app/Plugin/DataMigration4/Controller/Admin/ConfigController.php",60,"#0 /home/airconshop_shop/eccube-4.0.1/vendor/symfony/http-kernel/HttpKernel.php(151): Plugin\\DataMigration4\\Controller\\Admin\\ConfigController->index(Object(Symfony\\Component\\HttpFoundation\\Request), Object(Doctrine\\DBAL\\Connection))\n#1 /home/airconshop_shop/eccube-4.0.1/vendor/symfony/http-kernel/HttpKernel.php(68): Symfony\\Component\\HttpKernel\\HttpKernel->handleRaw(Object(Symfony\\Component\\HttpFoundation\\Request), 1)\n#2 /home/airconshop_shop/eccube-4.0.1/vendor/symfony/http-kernel/Kernel.php(200): Symfony\\Component\\HttpKernel\\HttpKernel->handle(Object(Symfony\\Component\\HttpFoundation\\Request), 1, true)\n#3 /home/airconshop_shop/eccube-4.0.1/index.php(74): Symfony\\Component\\HttpKernel\\Kernel->handle(Object(Symfony\\Component\\HttpFoundation\\Request))\n#4 {main}"] [POST, /penguinadmin/data_migration4/config, 131.147.87.32, https://shop.airconshop.jp/penguinadmin/data_migration4/config, Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/72.0.3626.119 Safari/537.36]
[2019-03-03 21:35:48] php.CRITICAL [uss0ikrloae2dfq9qqemnvutfk] [5d43f17] [1] [Symfony\Component\Debug\ErrorHandler:handleException:575] - Class 'wapmorgan\UnifiedArchive\UnifiedArchive' not found {"exception":"[object] (Symfony\\Component\\Debug\\Exception\\FatalThrowableError(code: 0): Class 'wapmorgan\\UnifiedArchive\\UnifiedArchive' not found at /home/airconshop_shop/eccube-4.0.1/app/Plugin/DataMigration4/Controller/Admin/ConfigController.php:60)"} [POST, /penguinadmin/data_migration4/config, 131.147.87.32, https://shop.airconshop.jp/penguinadmin/data_migration4/config, Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/72.0.3626.119 Safari/537.36]
[2019-03-03 21:35:48] php.INFO [uss0ikrloae2dfq9qqemnvutfk] [5d43f17] [1] [Symfony\Component\Debug\ErrorHandler:handleError:523] - User Deprecated: The "Sensio\Bundle\FrameworkExtraBundle\Configuration\Route" annotation is deprecated since version 5.2. Use "Symfony\Component\Routing\Annotation\Route" instead. {"exception":"[object] (ErrorException(code: 0): User Deprecated: The \"Sensio\\Bundle\\FrameworkExtraBundle\\Configuration\\Route\" annotation is deprecated since version 5.2. Use \"Symfony\\Component\\Routing\\Annotation\\Route\" instead. at /home/airconshop_shop/eccube-4.0.1/vendor/sensio/framework-extra-bundle/Configuration/Route.php:16)"} [POST, /penguinadmin/data_migration4/config, 131.147.87.32, https://shop.airconshop.jp/penguinadmin/data_migration4/config, Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/72.0.3626.119 Safari/537.36]
[2019-03-03 21:35:48] admin.INFO [uss0ikrloae2dfq9qqemnvutfk] [5d43f17] [1] [Eccube\Log\Logger:log:64] - LOGIC START ["data_migration4_admin_config"] [POST, /penguinadmin/data_migration4/config, 131.147.87.32, https://shop.airconshop.jp/penguinadmin/data_migration4/config, Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/72.0.3626.119 Safari/537.36]
[2019-03-03 21:35:48] php.INFO [uss0ikrloae2dfq9qqemnvutfk] [5d43f17] [1] [Symfony\Component\Debug\ErrorHandler:handleError:523] - User Deprecated: The "Eccube\Service\Composer\ComposerApiService" service is private, getting it from the container is deprecated since Symfony 3.2 and will fail in 4.0. You should either make the service public, or stop using the container directly and use dependency injection instead. {"exception":"[object] (ErrorException(code: 0): User Deprecated: The \"Eccube\\Service\\Composer\\ComposerApiService\" service is private, getting it from the container is deprecated since Symfony 3.2 and will fail in 4.0. You should either make the service public, or stop using the container directly and use dependency injection instead. at /home/airconshop_shop/eccube-4.0.1/vendor/symfony/dependency-injection/Container.php:282)"} [POST, /penguinadmin/data_migration4/config, 131.147.87.32, https://shop.airconshop.jp/penguinadmin/data_migration4/config, Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/72.0.3626.119 Safari/537.36]
[2019-03-03 21:35:48] php.INFO [uss0ikrloae2dfq9qqemnvutfk] [5d43f17] [1] [Symfony\Component\Debug\ErrorHandler:handleError:523] - User Deprecated: The "Eccube\Repository\BaseInfoRepository" service is private, getting it from the container is deprecated since Symfony 3.2 and will fail in 4.0. You should either make the service public, or stop using the container directly and use dependency injection instead. {"exception":"[object] (ErrorException(code: 0): User Deprecated: The \"Eccube\\Repository\\BaseInfoRepository\" service is private, getting it from the container is deprecated since Symfony 3.2 and will fail in 4.0. You should either make the service public, or stop using the container directly and use dependency injection instead. at /home/airconshop_shop/eccube-4.0.1/vendor/symfony/dependency-injection/Container.php:282)"} [POST, /penguinadmin/data_migration4/config, 131.147.87.32, https://shop.airconshop.jp/penguinadmin/data_migration4/config, Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/72.0.3626.119 Safari/537.36]
[2019-03-03 21:35:48] admin.DEBUG [uss0ikrloae2dfq9qqemnvutfk] [5d43f17] [1] [Eccube\Log\Logger:log:64] - Begin Transaction. [] [POST, /penguinadmin/data_migration4/config, 131.147.87.32, https://shop.airconshop.jp/penguinadmin/data_migration4/config, Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/72.0.3626.119 Safari/537.36]
[2019-03-03 21:35:48] admin.INFO [uss0ikrloae2dfq9qqemnvutfk] [5d43f17] [1] [Eccube\Log\Logger:log:64] - PROCESS START ["data_migration4_admin_config"] [POST, /penguinadmin/data_migration4/config, 131.147.87.32, https://shop.airconshop.jp/penguinadmin/data_migration4/config, Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/72.0.3626.119 Safari/537.36]
[2019-03-03 21:35:48] admin.INFO [N/A] [5d43f17] [N/A] [Eccube\Log\Logger:log:64] - INIT [] [POST, /penguinadmin/data_migration4/config, 131.147.87.32, https://shop.airconshop.jp/penguinadmin/data_migration4/config, Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/72.0.3626.119 Safari/537.36]