Having a similar issue on 2 different printers, an M300 and M200.
Prints will start fine but a few minutes into raft printing, will stop extruding. You can manually apply pressure to the filament and it will start coming through again, but stops as soon as pressure is released. Have tried all the following and problem continued:
Hot end and nozzle cleaned and checked.
Installed brand new hot end and nozzle.
At this point I noticed the motor on one machine was skipping/stuttering on every revolution, so I disassembled and cleaned debris from the gears. Made sure all parts were correctly put back together. That fixed the stutter, but the original problem persists.
Fairly confident this is not a blockage in the hot end because they are brand new zortrax components as well as the fact that I can apply pressure and get more material. Each time, the print will start but inevitably stop pushing material after a few minutes. It just seems like the motor cant grab hold of the filament. I am using proper filament for each machine.
Any possible solutions to this problem are greatly appreciated.