Facts about the Fiktionsbescheinigung:

1. It's not a permit, only a confirmation. Your expired residence permit stays valid anyway, even without a Fiktionsbescheinigung.

2. You are entitled to one. The LEA is breaking the law when refusing to issue them. It's just very slow and expensive to enforce that right.

https://allaboutberlin.com/guides/fiktionsbescheinigung