I started getting strings/hairs all over my parts when in the past it was working fine. I was using a different PLA so figured it was the settings and spent quite a bit of time trying to tune it in.
Well, I found it by accident. I changed from blue to red filament as I needed the blue for a customer order on another printer. The strings stayed blue. ????
Careful examination showed the heat block was slightly loose and filament was oozing UP, out the top, under the Kapton(tm) tape, down the back (still under the tape), and running down the back of the nozzle.
Tightened things up, removed all the tape and cleaned off the mess and retaped. Works great now.
"When you have eliminated the impossible, whatever remains, however improbable, must be the truth." Sherlock Holmes
Machine: "not-a-Prusa i4" (Sunhokey)
Filament: Polymaker PolyLite PLA