来自管理面板的Magento2备份给出了javascript错误

I am trying to backup from Magento admin panel but getting javascript error like this:

Uncaught TypeError: this.modal.find(...).validation is not a function at g.actionOk (backup.min.js:4) at $(/admin_sv7koc/backup/index/index/key/c31e7aed355659816bb6183c482181d177f3882a3fd19288cb4ebceeddbaf9ac/anonymous function).(anonymous function).click (https://truefarma.com/pub/static/version1551178986/adminhtml/Magento/backend/en_US/mage/adminhtml/backup.min.js:4:2035) at HTMLButtonElement.dispatch (jquery.min.js:338) at HTMLButtonElement.elemData.handle (jquery.min.js:311)

I am using Magento version: 2.2.2

Previously it was working fine but recently I have installed a new extension of Age gate popup (https://marketplace.magento.com/vsourz-age-verification.html)

Also, old backups are not showing in the list while backup files are there in the directory /var/backups.

I had tried following command:

php bin/magento setup:upgrade
php bin/magento setup:static-content:deploy
php bin/magento indexer:reindex
php bin/magento cache:clean

Thanks