Premiere pro not responding when i add sequence in a sequence

When I add a sequence into a sequence,

or sometimes, randomly (usually after adding one specific file onto a sequence timeline),

The hole project file becomes corrupted and not usable anymore.

This is the original Workspace Bar.

but when it's corrupted,

Workspace bar disappears. Of course I checked (turned on) Workspace. It just disappears.

Also,

Timeline becomes irresponsible.

I can't play the preview Video, can't click any properties, and etc.

Workspace also becomes irresponsible. I can't change workspace anymore.

Sometimes, I can click it, but still, it just won't work.

In the end, That little tiny dark grey square on top left corner is all i get for the project.

Once this happens, it stays permanently. It's either I have to go back to auto-saved file, or start from the bottom.

The worst thing about this is that

It slowly wrecks my project file, and at the point i realize it's here, i worked way too far to restart it.

Please tell me what makes this happen so at least i can avoid it,

or

please fix it. I had to throw away about 50 hours of work because of this problem.

It happens too often.