I don't have any idea why the objects loads so late, it's not normal at all.
The main objects should be loaded as soon as you enter within 8-9 nm of the airport so, even if your system was abnormally slow, there should be plenty of time to load them all when you have landed.
Only the smallest objects, like signs, lights, etc, have a reduced range, but the main buildings are loaded first.
Also, the software either works and load, or it doesn't. There really can't be a situation were it works, but it loads objects with so much delay.
The only thing I can think of, but it never happened so far, and nobody else reported it before, is that you have another addon that is sending so many Simconnect commands in such a short time, that has saturated the Simconnect communication channel and, since we use Simconnect calls to draw 3d objects, we might have been just cut out from it. But that's just an hypothesis, it might be useful trying to disable all the addon modules in both the EXE.XML and DLL.XML file, except the Addon Manager, and see if it improves, then re-enable one by one to find the eventual offender.
Have you tried acting on the "Anti Popup" Addon Manager slider, and see if it changes anything at various settings ?