Nothing changed, at all, during the pushback actual procedure between 2.9.1 and 2.9.4 so no, it can't be related to anything in GSX
With last update fps goes from 134 to 100/110 until push back stop.
Your frame rate is too high, you might just cause stuttering because you are forcing all Simconnect apps (not just GSX), to do extra work just to keep up with the too high fps. Try locking it at 50% of the monitor rate and see if you have an improvement.