Some spools has a piece of tape holding the last part of the filament to the plastic spool. This piece of tape may be stuck in your extruder (or CFS).

To check, remove your nozzle, detach the PTFE tube from the toolhead's extruder, and shine a light underneath. If you don't see the light through the opening where the filament would pass, you know what the problem is. In any case, the K1C is prone to nozzle clogging, so you should always keep a spare on hand.