I've noticed partial internal blockages when switching between PETG and PLA; ie' when purging, the new filament curves as it's coming out and I'll get inconsistent extrusion till it shakes a small fragment of the old filament out in the next print.
While cleaning filament helps, I think that's mostly as I can run it at 290°C to flush the remaining anything out... Plus it's a much longer filament swap process to do cleaning filament in between...
While regular nozzles are super cheap, the nextruder nozzles from Prusa aren't, especially the High Flow ones, and double especially the high flow Obxidian ones... The high flow nozzles also don't let you cold pull them the same way, which sucks...
When I started with my first printer, the flashforge A3, someone suggested having separate nozzles for PLA from PETG... I used to do this and it prevented many problems I'd been having from ever starting. I'm beginning to think about doing the same with my Mk4S, and having a separate hotend/nozzle combo for PETG, PLA, and PCCF that I can just swap...
So then I'll just need two new mk4 silicon socks in colours other than black so I can tell them apart....
My mk4s has just been replaced by Prusa. I've been chasing down first layer problems that manifested as load cell bed scan calibrations being haywire and filament blockage false positives.
After replacing just about every part of the nextruder 2 parts at a time, it started leading to the loveboard being the culprit, but after 6 weeks of troubleshooting, I asked for this to just be solved already, so they've JUST delivered the replacement.
So for me, it will be starting from scratch sith my mk4s, and figuring out what's needed.
Given I print mostly PETG structural parts, I'm imagining that I'll likely end up with 0.8mm as my default, and 0.6mm Obxidian as my abrasives nozzle. (I have been waiting to print PCCF for a while...)