Last night I installed the new Windows 10 KB4515384 update and P3D no longer starts starts. I get the splash screen for several seconds then the app terminates with no error message. I rebooted the PC and tried again to no avail. Uninstalling the Windows update solves the problem and P3D runs normal...

Do you have the Milviz WX Advantage Radar installed by any chance?
As of yesterday, it was not compatible with the hotfix and caused this exact symptom on my system. Renaming the DLL in the P3D modules folder did the trick.

Hi, If you monitor read/write activity with Process Monitor or similar tools, you will see, that this complete reload happens on these points regardless if you are on ground or 10000 ft above. A complete reload is triggered and no one knows why?!? I can't believe, that this can't be found. Someone ...

This happens to me as well in various locations.
When approaching most Flightbeam airports, Viewpoint Technologies KMHT, and Drzewiecki Designs NY airports.

A full scenery reload is done and it pauses my sim for 5-7 seconds. Only certain airports seem to trigger this phenomenon.