So weird. Some questions:
Are you running with the stock nozzle (0.4mm) or one of the other sizes?
Is the extruder intact? Do the extruder’s gears look to be in good condition and do they spin freely with no grinding sounds or catching, slipping or hesitation?
Are you using the AMS? If so, is it working correctly as well with no grinding sounds or catching, slipping or hesitation?
I suspect it may be a hang-up somewhere in the filament path above the extruder since you already eliminated that possibility by replacement.