The problem with unresponsive checkboxes in the WYSIWYG editor still persists. It is now confirmed and has been seen on two different platforms, and by two users. I believe that new information added to the GH bug report ( check boxes status cannot be changed (internittendly) · Issue #4490 · laurent22/joplin · GitHub ) today may provide sufficient insight into the nature of the problem, and may help to reproduce it.
This earlier post covers the same problem, and offers a short video.