Damn, I'm a few days late on seeing this, I might have been able to help, simple road fix with a drill bit or adding a few washers to push the MC out a hair. I had the same issue when pairing the booster with the Willwood MC. The pin was too long and was causing the pressure to build in the lines. They would completely lock after a few stops, I had to get out and relieve the lines to be able to move.
It took me a while to figure it out but lucky I was close to home testing it. I had to machine mine down and it worked great. I wish Willwood had the 1 1/16" bore tho, I will likely downsize the MC to 1" (stock) as I don't like the 1 1/8" bore, the pedal is way too stiff.
Good to see you got it fixed.