You may need to reset your cloud save to fix issues caused by corrupted saves or profiles.
Warning: Deleting the cloud save will wipe your logbook permanently. You will not lose the achievements already unlocked on this profile but progression towards achievements and the logbook information cannot be recovered.
- From your Steam Library, right-click on the Microsoft Flight Simulator icon
- Click on Properties
- Uncheck the "Keep Game saves in the cloud for Microsoft Flight Simulator" box
- Open (by default)
C:\Program Files (x86)\Steam\userdata
- Find the folder corresponding to your profile and delete the folder: Steam\userdata\usernumber)\1250410
- Restart Microsoft Flight Simulator
Follow the onboarding and launch a flight
If everything works, quit Microsoft Flight Simulator then you can re-enable Steam Cloud Sync.