RF brake locked up. Why?

As to the fluid movement the only time I saw any was when the pedal is pushed down and I was sure to tell my master pedal presser to go slowly.
That is your proof right there! About the first inch of pedal travel is taken up by slack, and then the piston closes the C-port. That is when you get the little roiling or fountain.
So now we know absolutely that the port is working.
When the pedal returns, fluid moves down into the chamber ready for the next application.
The second thing this proves, since you did NOT get a geyser, is that your system seems to be free of air.
I would be confident at this point to say that you do NOT have a hydraukic problem.
Neither of the wheels lock up completely so that's not a problem.
and this tells me your hoses are fine.
So now we are down to just three possibilities;
1) contact area,
2) contamination,
3) coefficient of friction.

#1 we already talked about, and
#2 that is to say grease,oil,or brakefluid on the linings,and
#3 is highly unlikely if you installed new shoes from the same box, with a reputable name on it.

As to #2,
In my younger years, I discovered that you can cook the contaminants out of the linings, in you mothers bake-oven; she'll never know I said. Hah! Mothers know everything......
I do appreciate all the help you've given me. If you ever get down to Houston, when the world stops being crazy, let me know. It's not a tourist mecca but there are things to see here and (fairly) close by. Mark
I try to be as helpful as possible.
And thanks for the offer