We were recently printing MatteraHackers PLA on an Ultimaker 3 Extended with Cura's recommended "Extra-Fine" setting. The first layer looked as expected, but the print core began to slowly under-extrude, and eventually no material was coming out of the nozzle. The support PVA was being printed without issues. I later found some of the PLA filament appeared to be "swollen" high in the print core, preventing it from being pushed through.
I swapped the print core for another AA 0.4 core we had around and the print finished successfully. Clearly there was a problem with the old core. Was it some how "back-heating" onto the filament, causing it to swell and get stuck? This was a print core that we have been using often for about a year. Do the print cores wear out and need replacing? I don't see any recommendations, by Ultimaker, for replacing print cores as part of regular maintenance.
Thanks for any tips you can give.