Docker Volume mssql_data won't create even though configured in config.yml

Hello,
I am running my bitwarten installation for more than a year without any problems on an ubuntu server with docker.
Since my last Ubuntu OS Update I had some problems with my mssql container that gets restartet in a loop. I found in bitwarden github issues (https://github.com/bitwarden/server/issues/531) the same problem.
The user there moved his bwdata from filesystem storage to docker volume storage by modifing database_docker_volume to true in config.yml.
I’ve changed that option, rebuilt and updated db, the initial issue got solved but there is no new docker volume that should have been created! The bwdata is still saved in the filesysten storage and there is no new mssql-data container.
I am a little bit confused where my vault is saved now.
Thanks for any help.