"undefined" in percent blocked after using watchtower for automatic updates

Expected Behaviour:

The "percent blocked" field displays a value in percent rather than the glancing "undefined" display. I am using pi-hole on my Synology NAS in Docker in version Pi-hole v5.3.1 Web Interface v5.5 FTL v5.8.1. The error occurs only after I have installed watchtower (https://mariushosting.com/synology-30-second-watchtower-install-using-task-scheduler-docker/) for updating.

Actual Behaviour:

Display of "percent blocked

Debug Token:

https://tricorder.pi-hole.net/bi7yvyd7ss

Don't use an automated update process.

The site you linked to doesn't seem to mention anything about Pi-hole so you need to ask the person that wrote the guide for help.

Ok. Thanks for the hint.
Have now created the Docker image again manually and have the same error. Therefore it is not due to watchtower

That's your next step.