well it is as far as I know unchanged from the default values of the mattermost docker image, so 100 connections.
I just changed it to 200 connections and restarted the docker container.
Same result, user deletion not working.
Therefore I just tested it with the old versions and max 100 connections:
I went back to version 5.27.1 => user deletion worked fine with the old CLI (mmctl user does not yet have the command delete)
Upgraded from 5.27.1 to version 5.28.1 => user deletion still worked fine, now even with mmctl
root@xyz:/var/xyz/mattermost# docker-compose exec app mmctl user delete <user_id> --confirm --local
Deleted user '<user_id>'
Upgraded again from 5.28.1 to 5.29.0 => user deletion is no longer working
root@xyz:/var/xyz/mattermost# docker-compose exec app mmctl user delete <user_id> --confirm --local
Unable to delete user '<user_id>' error: : Konnte die zu löschenden Nachrichten für den Benutzer nicht auswählen.,
So it really is a new problem that only does occur in 5.29.0 