Coming back to this....still getting a lot of thin hairs on my stock nozzle (removed prototype ruby) with Ultimaker brand filament. Would this be a symptom of needing to check my coupler or something? Did some atomic pulls and it's all clean and nicely shaped in there.

Beside the obvious temperature and retraction things, could it be that the nozzle is worn out? Once, I replaced nozzle to a new one and wow! That made a piece of the difference. Even though it only printed 80% PLA and the rest were ABS and PETG, in one year of medium usage any nozzle needs replacement.