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? Huh?
Neat joke that you are cracking! Lol! Relax, you are safe, legal and still exist. What has happened is that immigration was for some reason 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. If you just came in and had no previous residential status then you are only allowed to be / live here. You may not work!
Gee, with all this red tape, I guess I won't be able to travel, right?
Oh no! You are allowed travel with a Fiktionsbescheinigung! But be back in before the interim permit expires!! If not you might jeopardize your status. A Fiktionsbescheinigung is an (atypical) residence title pursuant to Art. 21 no. 2 Schengen Acquis, entitling you to travel in and out of Schengen area. Assuming you would not have such certificate, you would have a problem proving that you have a legal status here. This certificate has exactly that function. As a free person, you are allowed to travel. The main exception would be if there is a warrant of arrest out against you.
How often will I get such extension?
As many as necessary but as few as possible because the authorities love to have a clear status with you.
What I am to do when my extension expires?
Apply best ahead of time for another extension. In other words make another appointment and go to immigraiton.