Safari on OSX closes all tabs (crash?) after playing a YouTube video MacOS Catalina 10.15.7
Sometimes Safari (14.0.1) closes all open tabs after playing a YouTube video (most often in full-screen mode).
My typical scenario:

I have several opened tabs
I watch a youtube video in fullscreen mode in a tab
I close the tab using Cmd-W
I find Safari in the dock without any opened tabs

Is it a well-known bug or my local issue? Any ideas on how to fix/workaround it?
I follow to advice from the link and determine that Grammarly addon crash my Safri.