WebHook push not triggered on update via repository mirroring

Summary

I'm using the WebHook Push trigger to notify myself when then the project is updated via repository mirroring. However, for a few days, I'm experiencing that those WebHooks are not executed anymore. They do work when I use the test button, but they don't work when I push something or when the repository is updated via mirroring.

Steps to reproduce

Happened on existing projects. Not sure whether it is reproducible

Example Project

https://gitlab.com/aur-archlinux/mingw-w64-winpthreads

When a new commit is pushed to the build branch a new pipeline is triggered (and skipped as it says [ci skip] in the commit message). However, a second build should be triggered via WebHook Push which then builds the package.

This project may be used for testing. There is nothing in it which cannot be recreated in seconds.

What is the current bug behavior?

The WebHook Push is not executed. Neither on push nor when the project is updated via mirroring

What is the expected correct behavior?

The WebHook Push should be executed when either a new commit is pushed nor when the project is updated via mirroring

Output of checks

This bug happens on GitLab.com (example project is on GitLab.com)