TL;DR: A1 prints clean on every nozzle except the 0.2. Same spool, same slicer, same plate. On the 0.2 the extruder starts grinding the filament 10 to 50 layers in (deep gear marks on one side, chewed cross section, see photos). Replaced the entire hotend, did not fix it.
Setup
• Printer: Bambu Lab A1, coming close to 1000 hours on it
• Nozzle: 0.2, brand new full hotend swap (not just the brass tip). Original 0.2 had the same issue.
• Filament: Bambu PLA Basic, freshly opened sealed spool
• AMS: tested with and without, direct top feed, same result
• Slicer: 0.10mm custom layer height, Standard speed, defaults otherwise
• Print: multiple small parts on one plate
• Bed: smooth PEI, prepped with soap and water
• Cold pull: not done, but the whole hotend got swapped so the hot zone is brand new
What I've already ruled out
• Brand new full hotend assembly, same problem
• Tried a range of nozzle temps
• Same exact filament prints perfectly on 0.4, 0.6, and 0.8
• Pulled the AMS out, fed direct from the top, same problem
• Spool is fresh out of the bag
The pattern
Prints clean at first. Around layer 10 to 50 extrusion just dies. Extruder gear keeps spinning and chewing even though it's clearly gripping the filament. Photos attached: deep gear marks on one side of the filament and a chewed, narrowed cross section at the bite point. Feels like resistance gradually builds until the gear physically can't push anymore.
Bonus headache
Also getting first layer adhesion problems on the 0.2 profile at the same time, which makes me wonder if first layer Z is off and back pressure is killing me from the start.
Has anyone hit this exact combo? Grinding, only on the 0.2, brand new hotend, same filament fine on bigger nozzles. What was the actual fix for you?