FWIW, I found I'd get more consistent results always discarding the first extrusion. I assume it might have something to do with normalizing the temp of the aluminum block, or flushing overly soft filament out of the extruder.

Another thing we've seen is people trying to extrude faster than the extruder can keep up with, leading to inconsistent results. IIRC, 3mm/sec for 1.75mm filament and 1.5mm/sec for 3mm filament are about the upper end.