Why does buildah fail mounting overlays?

I am running buildah(quay.io/containers/buildah) in a gitlab CI/CD pipeline(kubernetes pod), but it fails building images. buildah bud . returns:

mount /var/lib/containers/storage/overlay:/var/lib/containers/storage/overlay, flags: 0x1000: permission denied
time="2023-05-03T13:02:06Z" level=warning msg="failed to shutdown storage: \"mount /var/lib/containers/storage/overlay:/var/lib/containers/storage/overlay, flags: 0x1000: permission denied\""
failed with exit code 125

Buildah inside of the container is running as root, and I made sure that the overlay module is loaded lsmod | grep overlay. I also read the [troubleshooting guide](https://github.com/containers/buildah/blob/main/troubleshooting.md) , but it only mentions issues in rootless mode. What could cause issues while mounting overlay filesystems? And which component could be causing the problem(kubernetes, buildah,gitlab-ci-cd,...)? Thanks in advance :)