FK8 with Water filled rear silencer restriction when hot

FK8 on the dyno with aftermarket exhaust that's causing restriction when hot due to water in the resonator.
I've seen this a few times now, and it's fine when exhaust is cold but when it gets really hot we hear a strange noise like a missfire or popping sound.
the hotter it gets the worse the noise to the point you can also feel a rumbling through the car.
moisture is also seen spitting out under power.
You would think it would evaporate off but under normal driving and with cool exhaust it appears its just not happening.
Solution had been advised as just drilling a small hole in bottom of the silencer.

[@Bravo101111]

What's the fuel pump duty and hpfp fuel pressure looking like in the hot run vs the cold run?

[@samanson2001]

This much of a problem with aftermarket exhausts on the FK8?

[@upbeatmantis86]

Depends on the type of aftermarket exhaust.. straight out ones are definitely better