I've had similar results with dirty filament. I had a roll that just sat around for a long time and had a thin film of dust on it. It printed fine for a while, but then the dust started to collect together and limited how much plastic could come out of the nozzle. I figured any dust would just pass through. It turns out that was a far too optimistic assumption. I was able to purge the dust jam by just heating the nozzle up very hot and running clean filament through the nozzle.