Bad quality printing(periodically small amount of plastic, plastic dots, and plastic web)

[Sautenich 0]

Hi Everyone!
We meet problem in our lab with printing quality with Ultimaker 3. Plastic PLA. We have already changed extruder, checked feed system, changed printing and feeding speed, but from time to time the problem comes back. 
Pls, look at the photos, maybe you have meet these problems before? What could you suggest in our case? What helped you with it?
Thx in advance ;)

Best,
Sautenich

[Hibino 3]

I had this issue before, it was caused by part blocked Nozzle can't squeeze out enough filament. Spent quite a lot time figuring out why nozzle always gets blocked and turns out that the ptfe tube where touching the nozzle is damanged and causing filament stuck there, you can try pull out your ptfe tube see if it is still in good shape.