Bugzilla

Sorry I haven't responded back to this.  I'm now currently using TB 91.1.2 (64 bit) and I'm still experiencing the issue.  A little more info though:  I have two monitors, a 24 inch HD monitor and a 43 inch UHD smart TV/monitor, both connected via HDMI on a video card.  They are configured in Windows in a top/bottom configuration with the 24 inch monitor on top as the main window.  

It seems that the issue only occurs when I open TB in the bottom window.  I'll get notifications on the bottom screen at the start, but later the notifications appear on the top screen.  Sometimes the notification on the top screen is only half visible as if the notification bubble isn't tall enough to contain the note and even cuts the TB logo in half.  Other times when the notification bubble is at this "half" height it may take several seconds for the info to populate it during which time TB will not respond.  Other times the notification bubble never populates and TB then must be closed via Task Manager or Process Explorer.  

I have noticed that TB normally runs with 2 instances of thunderbird.exe in the process tree, but when the error occurs there is only one.  Running TB in the top monitor does not seem to create the issue.  Running TB in Troubleshoot mode does not make any difference.  I have yet to try running it in Windows safe mode simply because the issue is random and may appear at the start of TB or several hours later.  I have added a PNG attachment of the empty bubble.