I am using a Mk2 for about half a year now and bought the Mk2.5 upgrade end of April. Since I was printing ABS until now, I wanted to learn to print PETG – but for the last few weeks I am only looking at failed first Layers (despite the very first print, a Benchy, with the Live-Z from ABS). Since then I tried nearly all values around the ABS-Live-Z (+-100), corrected the right side mesh bed leveling to be +50 now (the skirt was stopping on the right, so I raised the bed level correct until it nearly does not anymore, but also I am at the max). This is the first attached image, where the brim gets really squished at the right back side.
I also tried different temperatures for the original Prusa PETG and a little bit of flow. And – most of all, I looked at the print start with a speed down to 25% to slowly see, where it might fail, which I try to illustrate with the second image, that usually (with ABS) should read S-t-a-c-k-e-n – and I know it's a fine structure, _but_ it worked fine for all my test and prototypes for the last half year with ABS (using the same settings even for the first prints on the Mk2.5).
The problem seems to be that a little bit of PETG catches the nozzle and from than on a small blob smeares the PETG everywhere but not where it should got. And that seems to happen at a random point (sometimes it looks a bit better in the beginning, and as I said, the first Benchy printed well including the text on the bottom) – but I can't figure out why that is happening and it is not happening deterministically.
Any ideas what I can check besides 200nm of Live-Z checked through, temperatures, speed (all from 30% to 100% in 5% steps)? I am really lost in my approach to PETG and running out of ideas. I also tried with glue and without, with even more glue,...
Even more since the same Live-Z (even without the 50nm correction on the left) and the same 3D model, just sliced in Slic3r to the gcode for ABS works completely fine, that's what's wondering me the most.