Unusual print defect

As you can see in the pictures, the first half a dozes or so layers are printing, well strangely but only on the back and left side (Z perspective) and is more pronounced on the back. This is a new build (RAMPs using what was left of a DaVinci 1.0, Cura 3.6.0 and Marlin 1.1.x-bugfix). After some painstaking measurements, I was able to get my PEI bed adhesion working normally but the defect remains. I was hoping it was shifting during print etc. It's an enclosed print area and looking at the g-code through a couple of different rendering programs, it seems it should be fine. I've tried different spots on the print area as well to rule out something with the bed etc.



I've seen a lot of different defects in my own prints and in different print forums but this one takes the cake.

Can you confirm the hotend does make the actual motions? Or is the extruded filament taking a shortcut? Is the filament somehow constrained when the back is about to be printed? Is there a cooling fan not reaching some parts while being very strong on others? Is there an intermittent break in the hotend power lead?
Is it retracting on that corner? Are yoh using some kind of pressure advance compensation? Turned on but not calibrated?

That's all I could think of for now, hope it helps!

---

--
Kind regards
Imqqmi

NFAN CoreXY printer:
[reprap.org]