Linking to a video of the issue might be the most helpful, as I have no idea what this could be.
Basic troubleshooting steps could include resetting preferences:
Move the preferences folder (found in the Output folder) to the desktop, then restart X‑Plane and default preferences will be restored. If the default preferences do not fix your problem, you can simply replace them with the folder you moved to the desktop and restore your personalized settings.
And removing all add ons temporarily to see if any of them are causing it.