Activites overview stops the whole system

First look at the images to understand what happens

(if anybody can tell me how to upload a video here than it will be much better)

So the story is like this I clicked on the group then click outside the group to close it and then the system got stop.

Now what happens when it stops?:- I can use a mouse but mouse clicks don't work also keyboard doesn't work.

So ultimately I have to force shut down my laptop.

How often does this happen?:- probably depends on background task i.e., if I am using a heavy application like android-studio then it happens ones in 6 times

I don't want this to happen when I have unsaved work.