That is to be expected, as the created OAuth credentials are overwritten by your backup.
One way to deal with that, if you have no data in Rocket.Chat yet, is to trigger a RC reinstall, either by purging egroupware-rocketchat, or manually calling:
If you database is not running in a container as it’s the default for a 20.1 installation, you need to create a ~/.my.cnf file with root password AND in your case the host:
host = other.host
user = root
password = secret
database = egroupware
Test if you can access the database by simply typing
mysql without any parameter.