The only thing I might think of which might cause an additional strain on Simconnect, are the passengers, since they would require more commands sent in a very short time, to control their animations.
If that utility also sends lots of commands too, it's possible Simconnect simply cannot keep it it up so, and the errors you see (since they seem related to it) might be caused by that utility not being able to deal with the unexpected.
You can control how much strain on the sim passenger have, by lowering their density.
If this happens also when no passengers are visible, many even during a flight, then you can be sure GSX doesn't have anything to do with it, since during flight it sends just a very small packet of data to ask your position, speed and altitude and, if you are flying higher than 10k feet, it doesn't do any other communication with the sim so, is as low as you can, especially while cruising.