mysql access denied with bind mounts

[meinradr]

First of all I must say great project, I hope it keeps getting maintained. However, I have not been able to put it into production because of the following issue:

I setup elkarbackup with bind mounts to folders instead of volume mounts. Except of that, I'm using the exact same docker-compose.yml as in the example. When bringing up the containers with docker compose, the logs show the following issue:

elkarbackup_1  | 16:50:26 CRITICAL  [console] Error thrown while running command "elkarbackup:tick --env=prod". Message: "An exception occurred in driver: SQLSTATE[HY000] [1045] Access denied for user 'root'@'172.20.0.3' (using password: YES)" ["exception" => Doctrine\DBAL\Exception\ConnectionException { …},"command" => "elkarbackup:tick --env=prod","message" => "An exception occurred in driver: SQLSTATE[HY000] [1045] Access denied for user 'root'@'172.20.0.3' (using password: YES)"] ["user" => null,"user_email" => "","user_id" => "","user_name" => ""]
elkarbackup_1  | 
elkarbackup_1  | In AbstractMySQLDriver.php line 112:
elkarbackup_1  |                                                                                
elkarbackup_1  |   An exception occurred in driver: SQLSTATE[HY000] [1045] Access denied for u  
elkarbackup_1  |   ser 'root'@'172.20.0.3' (using password: YES)                                
elkarbackup_1  |                                                                                
elkarbackup_1  | 
elkarbackup_1  | In Exception.php line 18:
elkarbackup_1  |                                                                                
elkarbackup_1  |   SQLSTATE[HY000] [1045] Access denied for user 'root'@'172.20.0.3' (using pa  
elkarbackup_1  |   ssword: YES)                                                                 
elkarbackup_1  |                                                                                
elkarbackup_1  | 
elkarbackup_1  | In PDOConnection.php line 38:
elkarbackup_1  |                                                                                
elkarbackup_1  |   SQLSTATE[HY000] [1045] Access denied for user 'root'@'172.20.0.3' (using pa  
elkarbackup_1  |   ssword: YES)                                                                 
elkarbackup_1  |                                                                                
elkarbackup_1  | 
elkarbackup_1  | elkarbackup:tick [-h|--help] [-q|--quiet] [-v|vv|vvv|--verbose] [-V|--version] [--ansi] [--no-ansi] [-n|--no-interaction] [-e|--env ENV] [--no-debug] [--] <command> [<time>]
elkarbackup_1  | 

I check the database, the root user can be accessed from everywhere (¨% root¨). If I try to connect from the docker host to the database with the root user and the password, I run into an access denied error as well. I also tried with a mariadb database instead of the mysql, but I'm seeing the exact same issue.
What's the issue? And why does it behave differently with volume mounts and bind mounts.