I don't believe it would be an input high resistance other wise the light and motor would also trigger this behavior.
Now that it is isolated as the heater only I would check/trace the brown heater wire which is return. Since purple is hot all the time it should not be the issue since even with smoke off it could cause issues.
So make sure the heater element is not touch the smoke bowl on the Brown wire side, then make sure the brown wire doesn't have a pinch, or knick and touching chassis frames somewhere.
The load of the smoke unit is not so great that it would normally cause this. It only adds about .6 to .7 amps against a rectifier capable of 8 amps. Since you have removed one resistor, your pulling even less. So the wiring on the return side or the element touching the bowl are suspect issues to check. Than we move to the MUX in the engine. G
