Mushy brakes 4 life...

Not out of the question, bench bleeding can be a diagnosis as well
Pull it, drain it and then refill and bench bleed. Watch for bubbles in the fill ports. The push rod/pedal may need to be adjusted too, it may not be returning and allowing master to properly fill.
Not questioning your workmanship,but sometimes the simple things get overlooked.
The 59 i did brakes in were not right,ended up installing residual valves in the lines to hold pressure.
Also, e-brake can affect proper adjustment if levers arent fully returned.