▼テンプレート
[EC-CUBE] 4.0.2　4.0.0→4.0.1→4.0.2アップデート
[レンタルサーバ] さくらインターネット
[OS] 使用しているOS名、OS10.14.5
[PHP] 使用しているPHPのバージョン7.3.7
[データベース] 使用しているDB名、MySQL 5.7
[現象]
カード決済プラグインをアップデートした所、システムエラーが発生しましたの表示と以下のエラーログが

**************** Disable ****************
**************** Upgrade ****************
<warning>Deprecation warning: require.ec-cube/CategoryExtensionB is invalid, it should not contain uppercase characters. Please use ec-cube/categoryextensionb instead. Make sure you fix this as Composer 2.0 will error.</warning>
<warning>Deprecation warning: require.ec-cube/EccubeUpdater400to401 is invalid, it should not contain uppercase characters. Please use ec-cube/eccubeupdater400to401 instead. Make sure you fix this as Composer 2.0 will error.</warning>
<warning>Deprecation warning: require.ec-cube/EccubeUpdater401to402 is invalid, it should not contain uppercase characters. Please use ec-cube/eccubeupdater401to402 instead. Make sure you fix this as Composer 2.0 will error.</warning>
<warning>Deprecation warning: require.ec-cube/FacebookAdsExtention is invalid, it should not contain uppercase characters. Please use ec-cube/facebookadsextention instead. Make sure you fix this as Composer 2.0 will error.</warning>
<warning>Deprecation warning: require.ec-cube/MGSocialButton is invalid, it should not contain uppercase characters. Please use ec-cube/mgsocialbutton instead. Make sure you fix this as Composer 2.0 will error.</warning>
<warning>Deprecation warning: require.ec-cube/ProductContactB is invalid, it should not contain uppercase characters. Please use ec-cube/productcontactb instead. Make sure you fix this as Composer 2.0 will error.</warning>
<warning>Deprecation warning: require.ec-cube/SEO4 is invalid, it should not contain uppercase characters. Please use ec-cube/seo4 instead. Make sure you fix this as Composer 2.0 will error.</warning>
<warning>Deprecation warning: require.ec-cube/SlnPayment4 is invalid, it should not contain uppercase characters. Please use ec-cube/slnpayment4 instead. Make sure you fix this as Composer 2.0 will error.</warning>
<warning>Deprecation warning: require-dev.mikey179/vfsStream is invalid, it should not contain uppercase characters. Please use mikey179/vfsstream instead. Make sure you fix this as Composer 2.0 will error.</warning>
[166.6MiB/2.75s] ./composer.json has been updated
[167.0MiB/2.92s] <warning>Deprecation warning: require.ec-cube/CategoryExtensionB is invalid, it should not contain uppercase characters. Please use ec-cube/categoryextensionb instead. Make sure you fix this as Composer 2.0 will error.</warning>
[167.0MiB/2.92s] <warning>Deprecation warning: require.ec-cube/EccubeUpdater400to401 is invalid, it should not contain uppercase characters. Please use ec-cube/eccubeupdater400to401 instead. Make sure you fix this as Composer 2.0 will error.</warning>
[167.0MiB/2.92s] <warning>Deprecation warning: require.ec-cube/EccubeUpdater401to402 is invalid, it should not contain uppercase characters. Please use ec-cube/eccubeupdater401to402 instead. Make sure you fix this as Composer 2.0 will error.</warning>
[167.0MiB/2.92s] <warning>Deprecation warning: require.ec-cube/FacebookAdsExtention is invalid, it should not contain uppercase characters. Please use ec-cube/facebookadsextention instead. Make sure you fix this as Composer 2.0 will error.</warning>
[167.0MiB/2.92s] <warning>Deprecation warning: require.ec-cube/MGSocialButton is invalid, it should not contain uppercase characters. Please use ec-cube/mgsocialbutton instead. Make sure you fix this as Composer 2.0 will error.</warning>
[167.0MiB/2.92s] <warning>Deprecation warning: require.ec-cube/ProductContactB is invalid, it should not contain uppercase characters. Please use ec-cube/productcontactb instead. Make sure you fix this as Composer 2.0 will error.</warning>
[167.0MiB/2.92s] <warning>Deprecation warning: require.ec-cube/SEO4 is invalid, it should not contain uppercase characters. Please use ec-cube/seo4 instead. Make sure you fix this as Composer 2.0 will error.</warning>
[167.0MiB/2.92s] <warning>Deprecation warning: require.ec-cube/SlnPayment4 is invalid, it should not contain uppercase characters. Please use ec-cube/slnpayment4 instead. Make sure you fix this as Composer 2.0 will error.</warning>
[167.0MiB/2.92s] <warning>Deprecation warning: require-dev.mikey179/vfsStream is invalid, it should not contain uppercase characters. Please use mikey179/vfsstream instead. Make sure you fix this as Composer 2.0 will error.</warning>
[170.6MiB/3.30s] <warning>Dependency "ec-cube/plugin-installer" is also a root requirement, but is not explicitly whitelisted. Ignoring.</warning>
[170.4MiB/3.30s] Loading composer repositories with package information
[171.1MiB/4.28s] Updating dependencies (including require-dev)
[536.3MiB/23.46s] Nothing to install or update
[496.4MiB/23.52s] <warning>Package phpunit/phpunit-mock-objects is abandoned, you should avoid using it. No replacement was suggested.</warning>
[496.4MiB/23.52s] <warning>Package symfony/lts is abandoned, you should avoid using it. Use symfony/flex instead.</warning>
[497.2MiB/23.54s] Generating optimized autoload files
[499.8MiB/26.07s] <warning>Warning: Ambiguous class resolution, "Eccube\Entity\Category" was found in both "$baseDir . '/app/proxy/entity/Category.php" and "/home/xxxxx/www/xxxxxx/ec/src/Eccube/Entity/Category.php", the first will be used.</warning>
[499.8MiB/26.07s] <warning>Warning: Ambiguous class resolution, "Eccube\Entity\Product" was found in both "$baseDir . '/app/proxy/entity/Product.php" and "/home/xxxxx/www/xxxxxx/ec/src/Eccube/Entity/Product.php", the first will be used.</warning>
[500.0MiB/26.42s] <warning>Warning: Ambiguous class resolution, "Doctrine\Common\NotifyPropertyChanged" was found in both "/home/xxxxx/www/xxxxxx/ec/vendor/doctrine/common/lib/Doctrine/Common/NotifyPropertyChanged.php" and "/home/xxxxx/www/xxxxxx/ec/vendor/doctrine/persistence/lib/Doctrine/Common/NotifyPropertyChanged.php", the first will be used.</warning>
[500.0MiB/26.42s] <warning>Warning: Ambiguous class resolution, "Doctrine\Common\PropertyChangedListener" was found in both "/home/xxxxx/www/xxxxxx/ec/vendor/doctrine/common/lib/Doctrine/Common/PropertyChangedListener.php" and "/home/xxxxx/www/xxxxxxx/ec/vendor/doctrine/persistence/lib/Doctrine/Common/PropertyChangedListener.php", the first will be used.</warning>
[498.1MiB/27.09s] Memory usage: 498.06MiB (peak: 538.15MiB), time: 27.09s

**************** Schema Update ****************

これまでもプラグインをインストールするとよくエラー表示が出ました。
しかしインストールされたようでオーナーズストアに戻るとプラグイン一覧には表示されるので、有効化をクリックするとインターナルサーバーエラーになります。
インストールプラグイン一覧オーナーズストアに戻ると有効化されているといった状態だったので、今回のカード決済プラグインも同様のことをしたら、管理画面には入れるのですがサイトがメンテナンス表示になってしまいました。
どうしたら良いのかさっぱりわかりません。
ご指導よろしくお願いいたします。

EC-CUBEのインストールディレクトリを確認頂き「.maintenance」というファイルが残ってままになっていれば、削除してみると解消されるかもしれません。