Not the same machine(SX3), but I did have a few problems with a similar thing happening when the coolant was switching on!
I traced it back to the relay board sometimes going bonkers as it switched the relay. Without the pump load on the relay, the board was fine. Put the pump back on and I'd have my fingers crossed everything worked.
My solution was to put a lower 24VAC signal through the relay to control a proper power relay close to the pump. I've yet to see it exhibit the same problems since doing it.