If you haven't done that I would recommend to do this first, too. Maybe a (still working but) loose belt prevents it from staying in place. Worth a try.first replace the belts as this is the most common problem. Can you post a photo of the back of the mech.
Thats the back of itfirst replace the belts as this is the most common problem. Can you post a photo of the back of the mech.
Theres the front and topcheck that the idler tyre hasn't got a small split, you can see it from the front of the deck