Hi there. I'm sorry for your troubles, but have you tried running it as administer? To run it as administer go to where X-Plane 11 exe is located, and then right click and go under properties > Compatibility > Run as administer > apply > ok.
Here is an example of my file location on where my X-Plane exe is located. D:\SteamLibrary\steamapps\common\X-Plane 11 || Here is a screenshot on what it looks like:
http://prntscr.com/fqmunn
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Next, do you have any plugins, if so you should disable them until the problem is fixed.
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On Steam to check if any files are missing, go to your Steam Library and right click on X-Plane 11 and click Properties, then click Local Files and then click Verify Integrity Of Game Files and then let it do it's process to check if any files are missing. If files are missing, it will re-install them without you un-stalling and re-installing the game. *BEFORE YOU DO THIS make sure you delete any plugins or files you may have put in the X-Plane 11 files, and you can delete any folder in X-Plane11 and it will install them again for you during the process*
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If none of this works, I recommend to do any drivers updates on your computer and make sure everything is up to date.
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Hope this helps. C: