I can't explain it, but it sometimes happens for me, too, and no crashes/restarts are involved.  Since it seems to have zero impact on the functioning of NVDA I chalk it up to a quirk.

One of these days I need to check to see if both of those system tray icons would be responsive for the same running instance of NVDA.  Never bothered to check.
--

Brian - Windows 10 Pro, 64-Bit, Version 1909, Build 18363  

Power is being told you're not loved and not being destroyed by it.

       ~ Madonna