CREATE USER failed (mysql) after many successful upgrades

I've successfully updated this container many many times (running the famous
docker exec wallabag_container_name /var/www/wallabag/bin/console doctrine:migrations:migrate --env=prod --no-interaction
after each upgrade.)

This time is different and I get:
TASK [add mariadb user] bin dev entrypoint.sh etc home lib media mnt opt proc root run sbin srv sys tmp usr var fatal: [localhost]: FAILED! => {"changed": false, "msg": "(1396, \"Operation CREATE USER failed for 'wallabag'@'%'\")"}

in the docker logs.

Any help greatly appreciated.