I’m having the same or at least a similar issue. All animation files I created previously are impossible to work with since creating or moving keys causes Maya to freeze for several seconds. Everything is working fine when I add the same character in a new scene however, so I copied over the animations I need to work on into a new file. A lot of manual work, since Maya is horrible at copy&pasting keyframes, especially when anim layers are involved, but it’s the only workaround I could find.