Artifacts no longer get unlocked after Gitlab upgrade

Since we upgraded from 15.8.3. to 15.10. at the start of April we noticed that gitlab storage usage is inceasing every day.
While searching for the cause of this, we noticed a lot of old build artifacts.
Digging deeper we found that most of them seem to be marked as locked.
Despite reading through most of the documentation regarding artifact management we strugle to understand why they are not unlocked. Some hints would be appreciated!

We provide gitlab for our development teams, which use the pipelines to build java apps which then are put into docker container which then are deployed to our kubernetes clusters. Recently they installed dependabot which create lots of new builds.

Since upgrading to 15.10. old artifacts no longer get unlocked so they can expire / get deleted. I can´t find any mention of a change regarding artifacts in the releasenotes.
Most pipelines have set the artifacts to be kept for 2 hours only, some for a couple of days.
This problem is affecting all projects no matter the settings.

I already found that artifact housekeeping was disabled but as far as I understood the docs it is not responsible for unlocking artifacts. (enabled it anyway)

After heavy investigation I can´t seem to find a solution or even the reason for this.
To my understanding they should get unlocked after a new pipeline runs on the same ref or if the branch the pipeline came from is merged / removed?