Try my solution.
edit
Close msfs.
Go to:
MSFS MS Store ver
C:\Users\YOUR_USER_NAME\AppData\Local\Packages\Microsoft.FlightSimulator_8wekyb3d8bbwe\LocalState\MISSIONS\Custom
MSFS Steam ver.
C:\Users\YOUR_USER_NAME\AppData\Roaming\Microsoft Flight Simulator\LocalState\MISSIONS\Custom
Delete folder
CustomFlight
Run sim.