I will certainly admit I was wrong about one thing: apparently it wasn't the updated GSX that caused my problem with loading of consecutive FSDT airports, I have the same symptom after restoring from a system image made the day prior to running the new GSX updater.
After loading P3D Eglin (default scenario airport) and then load FSDT airports, the 2nd one I try to load takes about 10 min. - same if I keep trying additional FSDT airports.
Yet I consecutively loaded P3D Eglin (default scenario airport), FB KBOS, Orbx KEGE, FT KTPA, Orbx KPSO, FB KSFO, DD KSEA, UK2000 EGLL, and none of them took longer than 30 sec. to load.