I had this issue with PETG. When I inspected the filament I found about 50cm of it was “ribbed” (I think this is normal damage from the teeth of gears that feed it through to the printer). So I chopped that bit off. Also I was careful, this time, to chop the end of the filament at 45 degrees, and with the flat side of the cutters, as opposed to the angled side. Cutting with the flat side left a cleaner tip that wasn’t compressed into a fatter shape.
Printing worked fine after that