If you haven't already, use a vacuum bleeder. IMHO its a necessity after purging all the fluid. If your trying the normal way, I'm sure you have an air bubble in the line.
Not sure how it would work with hbb, but I've had vehicles/motorcycles with brakes that refused to bleed and I've had...
I rebuilt the rear calipers on my gen 3 and did not do anything special to bleed the brakes.
The guy said the problem started while he was working on the rear calipers. Have you verified the caliper works and the piston is not binding? Is fluid getting to the caliper?
Has anyone removed the rear tail pipe resonator on a gen 3? At least that's what I/m assuming it is. Is it louder, by how much?
I'm building a rear plate bumper and would like to remove the resonator and just stab a straight pipe though the plate bumper.