Need help understanding reasons for these print artefacts  

Need help understanding reasons for these print artefacts

EDIT: pics are not showing up, although they are visible in the edit? why?

----

Hello!

short version: printing the same model on my Mk2.5 comes out worse than on my Mk3S, but only on one far side of the print bed, see pictures. Both are on the same extruder revision. Why is this happening

longer version: I've started building keyboards this year, and tried my luck first with small ortholinear devices, for size, cost, complexity and curiosity reasons. I've modelled a housing that comes in two parts. The main upper part is printed upside down. 

Usually, I just drop the file into PrusaSlicer, select, "f" to place on desired face,  "a" for automatic arrangement, which always ends up horizontally on the print bed, with the high side in the back. I use .3 or .35 for quick prototypes. The grey one in the picture was printed in Prusament PETG with .3 layer height. Then its off to the printer, usually with no changes to a preset, especially for the first iterations.

What happens on the Mk2.5S is that the side of the part that ends up facing the far left side of the print bed comes out drastically worse than the right side of the same print, or either side of the same model when printed on my Mk3. It looks rougher and with more irregular lines, as if either the extruder or the positioning of it was having problems. I briefly considered cooling problems, but both Mk3S and Mk2.5S are on the same extruder revision. 

What is the reason for this?

The printer is about three years old, could maybe use more love, but has received upgrades and care. It also prints other models really nicely, as long as they don't straddle that area. 

Any ideas?

screenshot of PrusaSlicer with example configuration for my Mk2.5S Prusa PETG, .35, bad side of the print Prusament PETG, .3, bad side of the print Prusament PETG, .3, good side of the print