Each time I enter the manual mode I'm getting a stick error message in a red box. All is working fine and sometimes the message is vanishing after some time, it also vanishes when I switch to another mode. My controller is in Mode 1 and the right stick is changed by fastening the screws in the right way on the back as described (spring ineffective, with friction).

Any ideas what I can/need to do?

I think its a bug, Ive had it for month now in M mode, never had an issue with the controls being strange...

I posted my theory of why this happens here. There's also this post where someone said loosening the screw made the error go away.
In case you haven't seen it, I've posted photos of the controller's internals here. Some of the photos might help you see where the little internal buttons are located.

Duane Degn Posted at 4-18 08:01
I posted my theory of why this happens here. There's also this post where someone said loosening the screw made the error go away.
In case you haven't seen it, I've posted photos of the controller's internals here. Some of the photos might help you see where the little internal buttons are located.

Thanks, @Duane for this hint. As soon as we have some better weather here, I'll test what I can change with those two screws and if this affects.

I'm wondering how the TX is detecting that there should be a mechanical issue - you can measure the
resistance of the gimbals but this needs to be some kind of dynamic interpretation, or is there another build-in sensor?
Edit: I've looked into your disassembled picture - your interpretation of the little switch makes sense - this may be the sensor I was looking for.