I take it you're a Cypriot? I'm pretty certain that Cyprus is in a zone that is plagued by GPS jamming, does the satellite dropout increase the closer you get to the Turkish Cypriot border?
Have you run through a controller calibration?
I take it your drone isn't hammering upwards or downwards at full throttle, but creeping upwards (or the opposite).
Here's a question: ignoring the fact that the drone is constantly creeping...
Yes, I've stripped and reassembled various parts on the Mav. 2 airframe, the bottom cover has to be opened like a book cover after screw removal - there's a connector cable for the bottom lights and the O/A and I/R sensors... it will only lever...