I have an Ultimaker 2+ that has been causing me a few issues recently. At first I thought the tension on the feeder was too tight as the filament was just getting ground up at the back - however, every time I pulled the ground up filament out, the nozzle end of the filament had a plug about an inch up, disc shaped and usually split.
I'm thinking that this is an issue with the coupler, but just wanted folk's thoughts before I disassemble the hotend or get a new one. What do you think? Image attached.
Otherwise the printer prints perfectly for the first half hour or so, usually does the brim and then stops feeding & grinds up the filament.