Clean and lube all bearings, Do not know what your normal fixes are.
I would dissemble the Hot-end and check every part carefully skip if already complete.

Short story.
Had under extrusion an after a log troubleshooting experience found that Slicer filament diameter changed 1.75mm to 3mm causing under extrusion.

Attached Photo of under-extrusion
3mm - 1.75mm.jpg