Fine strands spanning gaps between separate features or parts.
hairs between partscobwebsspider webs
Ordered by how often each is actually responsible, not by how interesting it is. Work down the list.
Dry the spool before changing a single setting. On PETG and nylon this is the cause roughly 80% of the time, and tuning retraction on wet filament tunes around a problem you could have removed.
Run a temperature tower. Over-hot plastic runs out of the nozzle on its own.
Tune retraction distance ONLY, holding speed fixed. Changing both at once tells you nothing.
Raise travel speed. Less time in the air means less time to droop a string.