Extruder, Nozzle or Slicer problem？ please help

#1

Dobot Mooz2. i never had a successful print yet.
I heard slipping sound on the extruder. If I manually extrude/purge the filament PLA,ABS there is no such slipping issue.
But when printing, it always fails. I checked the nozzle temp and it seems alright. When I dis-assemble the extruder, I found filament stucked between the extruder and the nozzle entrance.
I am using Cura as slicer.
What might be wrong？ Please help.