It shifts about 10 degrees. I had the camera for about a month and I noticed it 3 or 4 times. The next time it shifts I'll try the "PTZ Reset"
If the camera gets snow or ice buildup in such a way to cause the camera to have trouble moving, the PTZ settings will get out align when a move attempt is made.
PTZ reset fixes this.
I've seen this with my PTZ.
During a snow storm, I try to position my ptz in such a way to minimize any buildup on it.
Sometimes that works, sometimes it doesn't.
Best bet, if you know it's bound up by snow/ice, don't try to use the PTZ. Let the sun do it's job.