Clutch pedal stuck down only after heavy breaking on track.

[SwedeGTI]

Hi!

Hopefully you can help me identify what is wrong here. My car is a manual Edition 30 running stage 2. With upgraded clutch Sachs performance and dual mass flywheel, car has only around 50k miles.
I have fully bleed and flush the brake fluid several times in the most careful way possible, added Motul RBF 600 DOT4, the one I got recommended to use on track.
The clutch pedal gets stuck down ONLY after heavy braking, mostly after the long straights on track. I pull it up with the foot and then it works like normal again for the whole lap (I got use to do that at this point)
I have only been able to replicate this on track, it usually happens after two or three laps, so it has to do with something heating up is my guess.
I am using a BBK from brembo with 4 pistons and 365mm discs, front, also bigger brakes on the back A4 S4 calipers.

[ZoliWorks]

Mine does the same but while spirited driving. It also only started happening after I switched to an R32 front/rear brake setup. Maybe it's the master cylinder for the brakes? The R32 is bigger than the GTI so it can move more fluid and I have not upgraded that.