Not sure how to tackle this exactly. Once the printer starts, the heater just doesn't want to be along for the ride. Could this be a connector or something else wiring going bad? Heater is new. Happy to post whatever you want to see from the duet - heater has been pid tuned.
The nearly instantaneous transients are too fast to be a heater problem. More likely, your temperature sensor has a loose crimp or other intermittent issues. Heater problems generally cause fairly smooth transients, since the real temperature doesn't slew all that fast.
Funny. I had this too. Just picking up the Hemera was enough to get the temp to spike up and the fan to come on. Clearly this was a heat sensor problem, not the heater. To resolve, I intended to check the connection from the PT100 to the board. While doing so I noticed the wires were really tight with no strain relief at all, so I moved things about a bit, unplugged, replugged, and haven't seen any similar problems since.
