This is a really weird issue. I haven't seen anything like this before, and AFAIK nothing similar has been reported.
Try resetting all application settings. The fastest way to do this is by deleting the PixInsight.ini (Windows, Linux) or PixInsight.plist (macOS) configuration file (while PixInsight is
not running, of course). You'll find this file on the same folder where you have your license file (see
FAQ 2.7 to learn where it is located on each platform). By doing this you'll lose all current settings, but your configuration will be reset to factory defaults the next time you launch the application. Let me know if this helps.