Ok, for me my previous theory around file encoding is confirmed on my system. For testing purposes I enabled logging for simconnect and the dll, then loaded the scenery as it was last night when it worked fine. This morning, still works fine. Then I loaded up the scenery.cfg file in this path:
C:\ProgramData\Lockheed Martin\Prepar3D v4 in notepad ++ and noted that it is in UTF-8 encoding.
Knowing that P3Dv4 likes UCS-2 LE BOM encoding, and any changes in the sim rewrites in this format, I changed the scenery.cfg file to this encoding type. No other changes. As you can see, this was the encoding type before LHBP installed itself:
Note the size difference between encoding types for the same file content:
I loaded up the sim and sure enough, no buildings. I exited the sim, changed the encoding back to UTF-8 and saved the file, no other changes. Loaded the sim and all buildings were back, loaded normally.
Im attatching the log files for all three scenarios, working, broken, then fixed again for your reference. In particular you will note that in the scenario where it is broken the error in the LHBP_Log file it says "
Scenery not active in P3D v4 scenery.cfg". Seems to be related to the dll's inability to ready and write in UCS-2 LE BOM encoding.