Copper gauze or brass brush is best to clean screw. Anything abrasive can scratch the screw and cause melt to stick resulting in more residence time and carbon build up. BTW your resin has very low MFI. Your heat settings may be too low based on resin and cycle time. You need to perform a melt temp test to see if you’re too cold on barrel. The carbon build up on screw may have been what kept the press running as it was until it got cleaned off.
Rick