I see.
Seems like the hot-end couldn’t keep the temperature stabilizing.
It’s hard to say the nozzle temperature was only effected by the voltage on the controller.
Did the nozzle temperature got N/A before? It seems like the thermistor may be not working fine.
You can check this thread http://forum.snapmaker.com/t/troubleshooting/155/186 . There’s a similar case like yours, you can check this first.
Hope this can help you.
Regards
Alan