I have an OMV4 Installation with Nextcloud, MariaDB and Let's Encrypt Dockers based on Techno Dad Life installation guide.
After updating my Nextcloud 16 Docker via the built-in update dialog in the Nextcloud UI, initially everything seemed fine. Then I got the message to exit "maintenance mode". After having done this by clicking in the UI, it seems not to be able to connect to the database anymore. The log file says:
PHP Fatal error: Uncaught Doctrine\DBAL\DBALException: Failed to connect to the database: An exception occurred in driver: SQLSTATE[HY000]  Network unreachable in /config/www/nextcloud/lib/private/DB/Connection.php:64#0 /config/www/nextcloud/3rdparty/doctrine/dbal/lib/Doctrine/DBAL/Connection.php(448): OC\DB\Connection->connect()#1 /config/www/nextcloud/3rdparty/doctrine/dbal/lib/Doctrine/DBAL/Connection.php(410): Doctrine\DBAL\Connection->getDatabasePlatformVersion()#2 /config/www/nextcloud/3rdparty/doctrine/dbal/lib/Doctrine/DBAL/Connection.php(354): Doctrine\DBAL\Connection->detectDatabasePlatform()#3 /config/www/nextcloud/3rdparty/doctrine/dbal/lib/Doctrine/DBAL/Connection.php(710): Doctrine\DBAL\Connection->getDatabasePlatform()#4 /config/www/nextcloud/lib/private/DB/Connection.php(151): Doctrine\DBAL\Connection->setTransactionIsolation(2)
Unfortunately I realized too late, that I should have updated the Nextcloud Docker itself somehow.
I hope so much that this can be solved. Thank you!