This happened on my 6D. The focusing screen holder dropped down with a lens attached to the camera. When I tried to remove the lens it would not turn enough to get it off. Shook the camera around some and was finally able to get the lens off. The screen had come out of the holder and was jamming the lens. The screen still works ok, but huge scratches in one corner. New screen should be here tomorrow. First time this has happened and I have one of the first release 6Ds. Not sure how this happens since you have to pull the tab to release the holder, not push it.
Gripped 6D, gripped 6D2, gripped 70D, 80D, 24-105 F4L, 50mm 1.8 STM, 55-250mm, 18-135mm, 60mm EF-S macro, 70-200 F4L IS, 400mm F5.6L, 18-55mm IS STM, Canon 85mm 1.8, Sigma 150-600mm C., Sigma 100-400mm C, Samyang 8mm 3.5 fisheye