I use an UM2. I am at my wits' end.
It started with warping but only at corners in the left/back quadrant. I adjusted and re-calibrated, I rotated my model to avoid that area and also chose one that had brims around the corners. Additionally, I loosened the spooled PLA to make sure the feeder wouldn't click. I'm not sure my measures were successful but now I observed something even weirder: one spot were underextrusion happens .
The surface is evenly cleaned, it doesn't look or feel different at that spot. How can this happen?