Can now confirm, that the bglmanx_fbeam.dat file is corrupt or something...
Have tried deleting the working (trouble-shooting) folder, and ran the setup for Addon Manager, which also downloaded the files online...
After which, the problem reverted, and no buildings showed up! After then replacing bglmanx_fbeam.dat file from Umberto's post, and overwriting it in FSX root, everything was working correctly again!
Thanks for all the help, and support, Umberto!