One ‘trick’ that might resolve the problem in advance of Sim Update 7 tomorrow is to try deleting the scenery index files and then re-run MSFS, which will regenerate the files.
For the MS Store version these files are located in:
C:\Users\username\AppData\Local\Packages\Microsoft.FlightSimulator_8wekyb3d8bbwe\LocalCache\SceneryIndexes
The files you want to delete are all called Filelistxxxx.dat
This may not work, but has resolved some loading issues for others with this issue.