Folks, I am getting good results by putting 1.75 into UM3 "as is" (no changes to the machine). This is what I am doing:
1. Temperature 215. (this is becuase the feeder has weaker grip on the filament. Make it easy for the feeder)
2. Layer height no more than 0.1mm on 0.4 head. On 0.8 head I allow myself to go higher (up to 0.4). With 0.25 I would not do it at all. (this is because you really want slower feeding). Decreasing print speed also works.
3. Use better filament holder, with thin axis and a silicon lube spray will not hurt. I designed my own: https://www.thingiverse.com/thing:4354166 . This will help the spool roll, further reducing the required feeding force.
4. In CURA, feeding rate set to 265% (which is, of course, diameter ratio squared).
5. Do yourself a favor and watch first 2-3 layers.
6. Same feeder, same PTFE tube, same print cores. No changes to the ultimaker. It just works.
With right settings I have no "feeder slips". However, they might be happening without me noticing, so maybe you should refrain from that from big high-quality prints. But honestly, I am getting perfect results even on fairly complex prints.
I had the exact same issue, and I noticed that if I immediately printed again then the print was perfect. I think I had skin oil on the BuildTak surface I was printing on which caused localized severe adhesion issues. Maybe try a quick back to back test?
For me: I was printing .2mm high by Xmm by Ymm flat squares to test ABL. I noticed that my first print after messing with the build surface would have that issue, and initially I thought maybe the print head was high or my leveling mesh was wrong... but then I noticed that without changing anything the next identical re-print would be perfect. Things would stay perfect until I enlarged the square or moved it and I might see the issue again. Now I'm just really careful with the surface and I don't see the issue very often.