While playing the animation if you delete all other keyframes except the first, Studio freezes or the animation editor widget freezes.
It messes up the widget it was on. For me, Studio doesn’t freeze after this, but it does break. If you attempt to save after it won’t finish, and will just be in that screen until you close it with task manager. Some people experience Studio freezing instead, though.
Video:
Here’s a picture of what happens to the window:
When you attempt to save:
Started happening as soon as you released this.