I got a new hotend for my Ender 3. When I start to 3D print a model, everything seems to be going well. After about 20 minutes or so the extrusion stops and the extruder motor can't push the filament through the hotend. I can usually fix the problem by pushing the filament in with my hand, but I don't know why it has such trouble pushing the filament out on its own after 20 minutes of printing.
I am printing with PETG filament, at about 200 °C. (I also got a new thermistor, and the readings on the new thermistor, could be about 20 degrees higher than they really are.)
The filament feeder knurled knob (shown below) hasn't been replaced since the day I got my 3D printer, and that may also be the culprit.