And if it were a controller assignment issue, it would happen 100% of the time after pushback, whereas my post states that it happens randomly.
Surely not.
Controller issues ( not necessarily "assignments" ) sometimes look "random" because controllers, by their very nature, can be affected by ambient factors like temperature, humidity and dust, at least those using standard pots.
GSX for MSFS never use Slew mode in any situation (like it did with P3D in the editors), this is quite easy to verify, because Slew mode in MSFS always changes the camera view to the Slew camera which is the reason why we are not using it anymore so, fact it's fixed by toggling Slew mode briefly, seems to indicate is not related to GSX.