Just to point 3: What could cause a "too much difference" when the computer is running and FSX is running at 1x simulation speed? For me it looks it does that constantly in that interval. I did not fly over time zones just a hour trip and even n ground during taxi it did it twice.
So if unsynchronizing helps that is a solution, but an intermediate.
I like the synch option as I don't have to do it via the FS menu anymore, but maybe it could be more tolerant if FSX is running internally too fast/too slow?
All in all it works very well, no problems except those three mentioned at the top of the thread.
Best
Alexander