Hi @ Unity Forum, One of our technical artists has bumped into a very strange issue while editing an animation. He simply started by editing an existing animation in the Animation Window and then hit the Play button. Immediately after clicking Play a part of the the animation window keyframes disappeared. It seems like some sort of a mask is hiding them because some of the keyframes are only partially visible and playing around with the zoom of the animation window can hide/show keyframes. The issue reproduces on Unity 2017.3.1p1 I've attached a video and a screenshot that demonstrates the issue. Anyone else bumped into this issue? Thanks, Aviv.