What the heck is this "Fiktionsbescheinigung"? This is the creepiest word I have ever heard in my life. When translating it, I get fiction certificate or certificate of fiction. Aha. Have I now lost my existence that I have become a fiction now?
Neat joke that you are cracking! Relax, you are safe, legal and still existing. for some reason, immigration was not in the position to finalize your application. It could be that they are still awaiting an answer from another authority, you have to still submit documents, or they have had no time to decide on your application or whatever.
Yeah. Great. And what are my rights?
Just as they were before – no more and no less. If you were allowed to work then continue doing so. If you just came in and had no previous residential status then you are only allowed to be / live here. You may not work! If you had a permit for employment or Blue Card that just expired after application of extension, you can continue working.
Gee, with all this red tape, I guess I won't be able to travel, right?
Yes and no! You are allowed travel with a Fiktionsbescheinigung based on §81 para. III AufenthG! If you travel, by all means be back in before the interim permit expires – if not you want to jeopardize your status.
How often will I get such extension?
As many as necessary but as few as possible. You are entitled to have a clear status at all times.
What I am to do when my extension expires?
Apply best ahead of time for another extension. In smaller municipalities, where you "know" your official, give them a call and ask. This approach might not work in cities.