did you also swap out the flex/hard line to the slave and replace it with Greg Browns flex line?
Did you pull the snap ring from the MC and back out the piston? do this with the vehicle level.

also verify the inlet port is turned so the hose has a continuous rise to the reservoir

 

I bought a new flex from Porsche. Kept the hard line.

I did back out the piston (rear end of the car on stand so not level)

Need to check the hose has a continuous rise to the reservoir (but I do not see why this can be an issue )

Thanks Stan

 

if the feed port isnt turned correctly then it will angle downwards and capture a pocket of air,
this will then get sucked into the MC and create the issue your having.
I suggest to remove the factory hard line and flex line and replace them with the insulated GB line,
its plug and play and forget it