Scratch this one. It was a Hardware Error. And by the "Hardware" i mean the MAZE.
I did the same maze again on a different surface, and the code runs flawlessly. I suppose it had a reflection or blind spot or something that threw the sensors off.
So anyone using Parallax Boebot and Linefollower-Kit: This Code is good.
Obviously not complete, but maze-solving with left-hand-on-wall rule is working as it should.
Thank you anyways wildbill. We could have spent a long time looking at telemetry. ^^