Hi SandervG,
thank you for your fast reply :-). Please see the picture for a succesful print and I also attached another picture of a bulgy filament end.
As far as I understand this problem, at some point the filament does not exit the nozzle anymore and the feeder keeps on feeding. Then the lump starts to grow inside the extruder until it becomes too big and the feeder starts grinding into the filament.
I have no idea why the extrusion stops after printing without any issues for a while. Very odd is also that after the problem occured, I perform the change material process (which means I remove the filament, cut off a bit and insert the same filament) the extrusion works just fine and I can start the next print (then, if it is a smaller one it prints without a problem).
I calibrated the bed, did the atomic method several times and cleaned the bowden tube.
Looking forward to your reply.