The issue has already been reported a couple of times, but so far no one was able to provide a step-by-step instruction to definitely reproduce the behaviour. See the thread below:
This is happening to me a couple of times now, luckily I was saving multiple copies of the file I was editing. You can't control Z out of it and double clicking not working. The file becomes corrupt and stuck in that state permanently. I wish I could take out the Isolate Group option in the right click menu because it is right next to Group which I use frequently....this is dangerous.
The issue has already been reported a couple of times, but so far no one was able to provide a step-by-step instruction to definitely reproduce the behaviour. See the thread below: