Brake servo problem

[Liamk]

So after the debacle of having the calipers on the wrong sides of the car I seem to have run into a potential servo problem. I’m quite happy there is no air in the system, pedal is hard and no excess travel with engine off but with engine running it has too much travel. It’s like the servo is getting too much vacuum. With engine running and vacuum pipe unplugged from servo pedal goes good again? Anybody had this before? All the searches I do seem to be the opposite with the pedal too hard? Thanks in advance.