The temperature is 16-19°C, that should not be too hot. and the bottom of the UM2 is quite well ventilated.
I guess I am going to take the head appart and check the teflon to be sure.
Enabling retractions on prints with way fewer retractions does not cause under-extrusion. This really starts happening over time. So retractions every 2-3 seconds seem to cause problems over time.
What you cannot see here is that the first 5mm the tube walls are thick. I saw under-extrusion at 6-7mm and paused the printer in order to make sure material was properly inserted. As you can see, the tube get better for a couple of centimeters (thin walls), then it starts again. But it does not deteriorate completely to the point of not printing anymore (like under-extrusion I had with the stock feeder).
Btw: Temperature is at 210°C
Could be that the steppers and/or the drivers get hot and start loosing steps and/or get locked? Though I could not expect this to happen after 10 layers or so, as in the picture, but could happen if the current is also high.
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