One Wheel Refuses to Bleed During Brake Bleed

An update...

After spending a lot of time trying to track down the correct ABS module for the car (and then having a junkyard ship me the wrong one), I've finally replaced the ABS module and bled the entire system again.

This has fixed only one of the two issues I had: I am now able to consistently bleed fluid out of the driver's rear wheel no matter if I start the car, leave it sitting, pull fuses, pull the battery etc. Woo! It previously wouldn't bleed (or only bleed intermittently) so that's nice.

However, when I do start the car, there is still zero brake pedal feel while the car is running. You can practically press the pedal down with your fingertip as it requires zero effort to do so. Turning the car off will let me pump up to a rock hard pedal again, and I can still bleed all brakes like normal, with no air bubbles and consistent fluid flow out of each caliper.

So now I'm really not sure what to make of this.

I've replaced the master cylinder and the ABS module. I know my brake booster is working correctly. Rear brake flex hoses and calipers are new and there's no system blockage or anything of the sort. Yet I still have no pedal feel and the car is not suitable to drive.

What gives? Any recommendations to try from here?