If you see such a warning, it can have several causes.

The main reason is that the lock file, which locks the migration process to prevent it from running twice, wasn't properly deleted. This can happen if the web server does not have write access to the specific path or if a migration failed for some reason.

You can try to delete the lock file manually if the warning persists after the maximum lifetime of the lock file (default: 300 seconds).

The lock file is located in the web server's /tmp folder. Depending on your system, this can be the actual path /tmp or a sandbox tmp folder. For example, on a standard Debian installation with Apache2, the /tmp folder exists in a systemd subfolder (like a sandbox). Therefore, you may find the migration lock file in a path like:

/tmp/systemd-private-09d13ddfc33841b5f63d1bb26a7e6a99-apache2.service-gZiG7a/tmp/.migration_running

To find this file more quickly, you can use the following command (example command for a standard Linux installation):

find /tmp -name ".migration_running" -type f -print

Returns for example: /tmp/systemd-private-09d13ddfc33841b5f63d1bb26a7e6a99-apache2.service-gZiG7a/tmp/.migration_running

You can delete this file with:

rm [the path shown from the find command]

Then reload the debug information page and check if the warning persists. If you still have problems to get it running, create a new discussion here.