BMG extruder under extrusion

The driving gear on the stepper shaft and the plastic gear are meshed too tightly. Loosen the bolts that attach the extruder and adjust i

Driving current is not high enough. With TMC drivers 800mA is high enough for most conditions.

Heat creep happened before and melted filament residuals clogged inside the heat break. Clean the heat break with a nozzle needle at printing temperature, or replace the heat break.

Retract too much and the softened & deformed filament clogs at the junction of heatbreak and nozzle. It depends on your filament, but for the BMG + Volcano combination, the slicer retraction settings of 0.4~0.8mm @ 40mm/s for PLA would be enough. Remember to check other retractions in pause.g, resume.g and in the end script of slicer.

The 3010 fan attached to the heat sink is not powerful enough. Use a fan with higher CFM.