maybe try do a bed tramming process with dial indicator? it’s like 20$ and 2 hours of print time but probably would solve your issue. The need of manually adjusting z offset is just very very strange if PLA works well. It’s a hint of the nozzle being pushed down by the extruder due to high restriction, either by not enough heating/fluidity or parcial clogs or other things like a loose hotend seat. Have you tried to print with the other nozzle?
My guesses:
- loose hotend seat: as pla flows easily it’s not gonna push the nozzle down. but for petg because it’s slightly harder to melt so it’s having a slightly higher nozzle pressure, resulting the nozzle to be pushed downwards by the extruder slightly.
- not enough heat (inaccurate nozzle temperature), so that the filament won’t be melt well, other users have found this problem but you would need some heat probes to get better measurement.
- other things like defective nozzle/partially clogged nozzle…
- bed not levelled well enough so combined with temperature difference it revokes the bed mesh…
Probably start by using the other nozzle to print and try without your z-offset adjustments, see if it works. Then tighten all those hotend seat & plate screws. Then if it still doesnt work do the manual bed tramming with dial indicators. Eventually, if it still doesn’t work, well it’s time to call support for a replacement of something…