Ok, I have done some more research. I first tried to do a repair but with no success. Then I tried a reset (see below image) and what happened was that the whole Microsoft.FlightSimulator_8wekyb3d8bbwe folder was emptied but the packages folder containing Official and Community remained intact. When I started the sim, the whole Microsoft.FlightSimulator_8wekyb3d8bbwe was repopulated again and the sim took ages to start. I probably lost all my bush trip history but I can live without that stuff.
Unfortunately the reset didn’t solve the main issue but the good thing is that I can exclude any corrupt file in that AppData folder. This folder seems to hold personal data and maybe also compiled wasm files. The real game data is probably completely stored in the Official folder so if there is something that is corrupt it must be in there, or at least that is my hypothesis right now. Of course there can be some other issue like hardware (I doubt it after a lot of investigation and I can fly bush trips without issues), some other software (I doubt it because I haven’t installed any new software since this issue appeared), or some communication issue where my computer cannot ping a server somewhere. My primary suspect is though the core sim files or something I have bought from the Market Place. The latest thing I bought was the DCH-5 which I flew last Saturday though.
The question is how to proceed. Should I uninstall all paid airports or should I start with any aircraft? The whole sim seems to be very data driven to a huge extent. Scenery and aircraft are made up from definitions stored in different files in the Official folder and even more details are coming from the cloud. I haven’t changed any code (I haven’t seen any software update from MS after I bought the DCH-5) so maybe some data file is corrupt but why?? If they contain plain data they should only be read and a sudden death of the sim process should not cause a corrupt file.
This is a big mystery. I doubt a reinstall will fix this. Maybe the only option left is to wait for SU12 and meanwhile fly all the bush trips (they work fine!!) to keep the abstinence level low. I guess no help from MS is expected. If SU12 doesn’t fix it, then I’m out of options. No more community flying or adventures around the globe 
