It however does not have issues maintaining the temperature when it’s not actually printing. I can set my hotend to 215 before beggining my print and it’s happy to sit there.
Other problems with it include under extrusion and extruder skipping, as it seems to have troubles pushing the filament out.
What does this sound like it could be? Does it sound like a blockage? Could a blockage cause temperature issues? I have already tried turning off the part cooling fan as I had a similar issue with that a while back but that has no made a difference it seems.
That looks like a failing thermistor or heater cartridge. You might want to swap out both the thermistor and the heater cartridge at the same time. Had something similar happen to me and it turned out the failure of the one, likely influenced the other to wear out prematurely. The cartridge wasn’t exactly broken, but seemed to have a less consistent response curve. You can test them separately, but they are cheap enough that it is not worth the hassle