After reboot: SQLSTATE[HY000] [1045] Access denied for user

I have an issue with error message SQLSTATE[HY000] [1045] Access denied for user: Internal Server Error on RPI

The reason for this error is a wrong

  'dbpassword' => 'XXXX',

in this file: /path/to/nextcloud/config/config.php
The solution is easy -> change the password to the correct one.

But, after reboot the password is reset to the old wrong one and I have to change it manually in the config file again.

Please describe IN DETAIL how you’ve set-up Nextcloud on your Raspberry Pi, what packages/versions you’re using, etc., etc.

I followed this manual:

Details about my system can be found here: Internal Server Error on RPI

Die Suchfunktion zeigt mir folgendes:

Very interesting., thank you.
I already had the idea to search for the error message but couldn’t find a solution.
Feel free to let me know if you have found a solution or have any idea that might help.