Found a reproducible crash in Adobe Reader DC -both free and Pro version (likely 100% occurrence in core i7 U series 7th, 8th gen, Xeon Gold, AMD Athlon):

Prerequisite:
Under PREFERENCES>GENERAL, "Open documents as new tabs in the same window (require relaunch)" is UNCHECKED. This means every time I open a new PDF file, it will appear as a new window instead of nested tabs.
- Opening a PDF file with highlighter markups
- Opening a comment pane of that file
- Then opening a new PDF window (from the same file): Window>New window
- Opening another PDF file or more to test the bugs (they will all close when bug is triggered).

If you close the first PDF (the one with two same windows) by clicking the X close button STARTING from the one with comment pane previously opened (even though now comment pane already closed, crash still happens), then closing the second windows of the same PDF file WILL cause all opened PDF to close (CRASH) without any messages.

Strangely, if you close the one without previously opened comment pane and then the one with comment pane, then you can avoid this crash.

If BOTH windows have comment panes, no matter which window you close with X button, it will trigger crash for the other PDF windows.

Please see the uploaded video.