Brake issue and I am at a total loss.

General rambling from the old and senile.

It might be possible that you have something wrong with the master / pushrod piston. Basically you will have to carefully inspect and manually feel the pedal.

"What you want" is to be absolutely certain that the pedal / linkage / pushrod is allowing the master piston to fully return all the way to the clip retaining the piston in the bore.

I'm not "real" sure what I'd do because I've never been where you are.

One thing is to get on the adjusters and tighten up all 4 good and tight to eliminate the shoes as a problem

Another thing might be to buy some 3/16 inverted flare plugs and unions so you can cap off the lines, that is pull the lines loose where the metal lines connect to the hoses. Cap /plug off the metal lines. You should be able to bleed right there at the cap and produce a "rock hard" pedal.

I would review what you've done with / at the master for bleeding it. There is some but not great possibility that the master is defective. I'd think this is low on the list.

Detail "just how" you are bleeding. If you are somehow allowing air BACK IN when releasing the pedal, this might account for the problem.