▼テンプレート
[EC-CUBE] 4.0.4
[レンタルサーバ] CoreServer
[OS] Ubuntu
[PHP] 7.1.33
[データベース] MySQL 5.7.29
[WEBサーバ] Apache
[ブラウザ] Firefox/82.0
[導入プラグインの有無] 無し（これから）
[カスタマイズの有無] 無し
[現象]
　管理画面-オーナーズストアから「関連商品プラグイン」というプラグインをインストールしようとすると、「インストール確認」というタイトル及び「システムエラーが発生しました」という内容のダイアログが表示され、インストールができません。
この状態ではブラウザの閉じるボタンがすぐには反応しないのですが、しばらく放置していると、InternalServerErrorの画面になります。
site---logには以下のように残っています。

[2020-11-16 11:28:15] app.INFO [N/A] [11ef253] [1] [Eccube\Log\Logger:log:68] - PROCESS END ["admin_store_plugin_install_confirm"] [GET, /kanri/store/plugin/api/install/1761/confirm, xxx.xxx.xxx.xxx, http://www.we-ne.site/kanri/store/plugin/api/search/page/5, Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:82.0) Gecko/20100101 Firefox/82.0]
[2020-11-16 11:28:15] admin.INFO [96ec378f] [11ef253] [1] [Eccube\Log\Logger:log:64] - LOGIC END ["admin_store_plugin_install_confirm"] [GET, /kanri/store/plugin/api/install/1761/confirm, xxx.xxx.xxx.xxx, http://www.we-ne.site/kanri/store/plugin/api/search/page/5, Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:82.0) Gecko/20100101 Firefox/82.0]
[2020-11-16 11:28:15] admin.INFO [96ec378f] [11ef253] [1] [Eccube\Log\Logger:log:64] - <warning>Deprecation warning: require.ec-cube/ProductDisplayRank4 is invalid, it should not contain uppercase characters. Please use ec-cube/productdisplayrank4 instead. Make sure you fix this as Composer 2.0 will error.</warning> <warning>Deprecation warning: require.ec-cube/ProductReview4 is invalid, it should not contain uppercase characters. Please use ec-cube/productreview4 instead. Make sure you fix this as Composer 2.0 will error.</warning> <warning>Deprecation warning: require.ec-cube/Recommend4 is invalid, it should not contain uppercase characters. Please use ec-cube/recommend4 instead. Make sure you fix this as Composer 2.0 will error.</warning> <warning>Deprecation warning: require.ec-cube/RelatedProduct4 is invalid, it should not contain uppercase characters. Please use ec-cube/relatedproduct4 instead. Make sure you fix this as Composer 2.0 will error.</warning> <warning>Deprecation warning: require.ec-cube/Securitychecker4 is invalid, it should not contain uppercase characters. Please use ec-cube/securitychecker4 instead. Make sure you fix this as Composer 2.0 will error.</warning> <warning>You are running composer with xdebug enabled. This has a major impact on runtime performance. See https://getcomposer.org/xdebug</warning> <warning>Warning from https://repo.packagist.org: You are using an outdated version of Composer. Composer 2.0 is now available and you should upgrade. See https://getcomposer.org/2</warning> name : ec-cube/plugin-installer descrip. : EC-CUBE plugin installer. keywords : versions : 0.0.8, 0.0.7, 0.0.6 type : composer-plugin license : MIT License (MIT) (OSI approved) https://spdx.org/licenses/MIT.html#licenseText source : [git] https://github.com/EC-CUBE/eccube-plugin-installer.git 6185cd43ae0dd0423bebc9bb900d096356340f80 dist : [zip] https://api.github.com/repos/EC-CUBE/eccube-plugin-installer/zipball/6185cd43ae0dd0423bebc9bb900d096356340f80 6185cd43ae0dd0423bebc9bb900d096356340f80 names : ec-cube/plugin-installer autoload psr-0 Eccube => src/ requires composer-plugin-api ^1.0 {"command":"info","package":"ec-cube/plugin-installer","version":"~0.0.6","--available":true,"--working-dir":"/virtual/ansuz/public_html/www.we-ne.site","--no-ansi":true} [GET, /kanri/store/plugin/api/install/1761/confirm, xxx.xxx.xxx.xxx, http://www.we-ne.site/kanri/store/plugin/api/search/page/5, Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:82.0) Gecko/20100101 Firefox/82.0]
[2020-11-16 11:28:12] admin.INFO [96ec378f] [11ef253] [1] [Eccube\Log\Logger:log:64] - <warning>Deprecation warning: require.ec-cube/ProductDisplayRank4 is invalid, it should not contain uppercase characters. Please use ec-cube/productdisplayrank4 instead. Make sure you fix this as Composer 2.0 will error.</warning> <warning>Deprecation warning: require.ec-cube/ProductReview4 is invalid, it should not contain uppercase characters. Please use ec-cube/productreview4 instead. Make sure you fix this as Composer 2.0 will error.</warning> <warning>Deprecation warning: require.ec-cube/Recommend4 is invalid, it should not contain uppercase characters. Please use ec-cube/recommend4 instead. Make sure you fix this as Composer 2.0 will error.</warning> <warning>Deprecation warning: require.ec-cube/RelatedProduct4 is invalid, it should not contain uppercase characters. Please use ec-cube/relatedproduct4 instead. Make sure you fix this as Composer 2.0 will error.</warning> <warning>Deprecation warning: require.ec-cube/Securitychecker4 is invalid, it should not contain uppercase characters. Please use ec-cube/securitychecker4 instead. Make sure you fix this as Composer 2.0 will error.</warning> <warning>You are running composer with xdebug enabled. This has a major impact on runtime performance. See https://getcomposer.org/xdebug</warning> {"command":"config","setting-key":"repositories.eccube","setting-value":["{\"type\":\"composer\",\"url\":\"https:\\/\\/package-api.ec-cube.net\",\"options\":{\"http\":{\"header\":[\"X-ECCUBE-KEY: e42cu8CF2TWA0NlWTxl5l8E1rBBiMM2VQjdpc19O\"]}}}"],"--working-dir":"/virtual/ansuz/public_html/www.we-ne.site","--no-ansi":true} [GET, /kanri/store/plugin/api/install/1761/confirm, xxx.xxx.xxx.xxx, http://www.we-ne.site/kanri/store/plugin/api/search/page/5, Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:82.0) Gecko/20100101 Firefox/82.0]
[2020-11-16 11:28:11] admin.INFO [96ec378f] [11ef253] [1] [Eccube\Log\Logger:log:64] - <warning>Deprecation warning: require.ec-cube/ProductDisplayRank4 is invalid, it should not contain uppercase characters. Please use ec-cube/productdisplayrank4 instead. Make sure you fix this as Composer 2.0 will error.</warning> <warning>Deprecation warning: require.ec-cube/ProductReview4 is invalid, it should not contain uppercase characters. Please use ec-cube/productreview4 instead. Make sure you fix this as Composer 2.0 will error.</warning> <warning>Deprecation warning: require.ec-cube/Recommend4 is invalid, it should not contain uppercase characters. Please use ec-cube/recommend4 instead. Make sure you fix this as Composer 2.0 will error.</warning> <warning>Deprecation warning: require.ec-cube/RelatedProduct4 is invalid, it should not contain uppercase characters. Please use ec-cube/relatedproduct4 instead. Make sure you fix this as Composer 2.0 will error.</warning> <warning>Deprecation warning: require.ec-cube/Securitychecker4 is invalid, it should not contain uppercase characters. Please use ec-cube/securitychecker4 instead. Make sure you fix this as Composer 2.0 will error.</warning> <warning>You are running composer with xdebug enabled. This has a major impact on runtime performance. See https://getcomposer.org/xdebug</warning> <warning>Warning from https://repo.packagist.org: You are using an outdated version of Composer. Composer 2.0 is now available and you should upgrade. See https://getcomposer.org/2</warning> name : ec-cube/RelatedProduct4 descrip. : 関連商品プラグイン keywords : versions : 4.0.1 type : eccube-plugin source : [] dist : [tar] https://package-api.ec-cube.net/ec-cube/RelatedProduct4/4.0.1/RelatedProduct4-4.0.1.tgz names : ec-cube/relatedproduct4 requires ec-cube/plugin-installer ~0.0.6 {"command":"info","package":"ec-cube/RelatedProduct4","version":"4.0.1","--available":true,"--working-dir":"/virtual/ansuz/public_html/www.we-ne.site","--no-ansi":true} [GET, /kanri/store/plugin/api/install/1761/confirm, xxx.xxx.xxx.xxx, http://www.we-ne.site/kanri/store/plugin/api/search/page/5, Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:82.0) Gecko/20100101 Firefox/82.0]
[2020-11-16 11:27:59] admin.INFO [96ec378f] [11ef253] [1] [Eccube\Log\Logger:log:64] - <warning>Deprecation warning: require.ec-cube/ProductDisplayRank4 is invalid, it should not contain uppercase characters. Please use ec-cube/productdisplayrank4 instead. Make sure you fix this as Composer 2.0 will error.</warning> <warning>Deprecation warning: require.ec-cube/ProductReview4 is invalid, it should not contain uppercase characters. Please use ec-cube/productreview4 instead. Make sure you fix this as Composer 2.0 will error.</warning> <warning>Deprecation warning: require.ec-cube/Recommend4 is invalid, it should not contain uppercase characters. Please use ec-cube/recommend4 instead. Make sure you fix this as Composer 2.0 will error.</warning> <warning>Deprecation warning: require.ec-cube/RelatedProduct4 is invalid, it should not contain uppercase characters. Please use ec-cube/relatedproduct4 instead. Make sure you fix this as Composer 2.0 will error.</warning> <warning>Deprecation warning: require.ec-cube/Securitychecker4 is invalid, it should not contain uppercase characters. Please use ec-cube/securitychecker4 instead. Make sure you fix this as Composer 2.0 will error.</warning> <warning>You are running composer with xdebug enabled. This has a major impact on runtime performance. See https://getcomposer.org/xdebug</warning> {"command":"config","setting-key":"repositories.eccube","setting-value":["{\"type\":\"composer\",\"url\":\"https:\\/\\/package-api.ec-cube.net\",\"options\":{\"http\":{\"header\":[\"X-ECCUBE-KEY: e42cu8CF2TWA0NlWTxl5l8E1rBBiMM2VQjdpc19O\"]}}}"],"--working-dir":"/virtual/ansuz/public_html/www.we-ne.site","--no-ansi":true} [GET, /kanri/store/plugin/api/install/1761/confirm, xxx.xxx.xxx.xxx, http://www.we-ne.site/kanri/store/plugin/api/search/page/5, Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:82.0) Gecko/20100101 Firefox/82.0]
[2020-11-16 11:27:58] admin.INFO [96ec378f] [11ef253] [1] [Eccube\Log\Logger:log:64] - http get_info {"url":"https://package-api.ec-cube.net/plugin/1761","content_type":"application/json;charset=UTF-8","http_code":200,"header_size":413,"request_size":191,"filetime":-1,"ssl_verify_result":0,"redirect_count":0,"total_time":0.59033800000000003,"namelookup_time":0.0041289999999999999,"connect_time":0.023438000000000001,"pretransfer_time":0.066320000000000004,"size_upload":0,"size_download":845,"speed_download":1431,"speed_upload":0,"download_content_length":-1,"upload_content_length":0,"starttransfer_time":0.59029900000000002,"redirect_time":0,"redirect_url":"","primary_ip":"133.242.233.183","certinfo":[],"primary_port":443,"local_ip":"202.172.26.42","local_port":59146,"message":""} [GET, /kanri/store/plugin/api/install/1761/confirm, xxx.xxx.xxx.xxx, http://www.we-ne.site/kanri/store/plugin/api/search/page/5, Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:82.0) Gecko/20100101 Firefox/82.0]
[2020-11-16 11:27:58] admin.INFO [96ec378f] [11ef253] [1] [Eccube\Log\Logger:log:64] - LOGIC START ["admin_store_plugin_install_confirm"] [GET, /kanri/store/plugin/api/install/1761/confirm, xxx.xxx.xxx.xxx, http://www.we-ne.site/kanri/store/plugin/api/search/page/5, Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:82.0) Gecko/20100101 Firefox/82.0]
[2020-11-16 11:27:58] php.INFO [96ec378f] [11ef253] [1] [Symfony\Component\Debug\ErrorHandler:handleError:532] - 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 /virtual/ansuz/public_html/www.we-ne.site/vendor/symfony/dependency-injection/Container.php:282)"} [GET, /kanri/store/plugin/api/install/1761/confirm, xxx.xxx.xxx.xxx, http://www.we-ne.site/kanri/store/plugin/api/search/page/5, Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:82.0) Gecko/20100101 Firefox/82.0]
[2020-11-16 11:27:58] admin.INFO [96ec378f] [11ef253] [1] [Eccube\Log\Logger:log:64] - PROCESS START ["admin_store_plugin_install_confirm"] [GET, /kanri/store/plugin/api/install/1761/confirm, xxx.xxx.xxx.xxx, http://www.we-ne.site/kanri/store/plugin/api/search/page/5, Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:82.0) Gecko/20100101 Firefox/82.0]
[2020-11-16 11:27:58] request.INFO [N/A] [11ef253] [N/A] [Symfony\Component\HttpKernel\EventListener\RouterListener:onKernelRequest:123] - Matched route "admin_store_plugin_install_confirm". {"route":"admin_store_plugin_install_confirm","route_parameters":{"_controller":"Eccube\\Controller\\Admin\\Store\\OwnerStoreController::doConfirm","id":"1761","_route":"admin_store_plugin_install_confirm"},"request_uri":"http://www.we-ne.site/kanri/store/plugin/api/install/1761/confirm","method":"GET"} [GET, /kanri/store/plugin/api/install/1761/confirm, xxx.xxx.xxx.xxx, http://www.we-ne.site/kanri/store/plugin/api/search/page/5, Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:82.0) Gecko/20100101 Firefox/82.0]
[2020-11-16 11:27:58] admin.INFO [N/A] [11ef253] [N/A] [Eccube\Log\Logger:log:64] - INIT [] [GET, /kanri/store/plugin/api/install/1761/confirm, xxx.xxx.xxx.xxx, http://www.we-ne.site/kanri/store/plugin/api/search/page/5, Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:82.0) Gecko/20100101 Firefox/82.0]

ec-cubeをインストールして、すぐにプラグインをインストールしても、状況は変わりません。
何が原因でインストールできないのでしょうか？
また対応方法を教えていただけますと助かります。