Construct 0.99.42
I have more luck reproducing this in a cap with many objects, sprites, and backgrounds.. I tried to narrow it down, once, but couldn't figure it out. It doesn't happen all of the time, I think..
Steps to reproduce:
In a sprite with multiple animations, try deleting one of the animations.
Construct may freeze on me when I do this.
It's also happening when I try to delete an animation angle on sprites.
A workaround, for either the delete-animation or delete-animation-angle freezes, which has worked for me _every time_ is to rename the animation before deleting it or one of its angles. Such as if I have an animation "Attack", I can rename it to "Attacka" then delete it without freezing.