FX Fx Wildcat mk 3 is difficult to fill

Hi guys

I hope you can help me. Among other things, I have a Fx Wildcat mk3 in.25. And my problem is, when filling, the air comes out at the fill probe, and so the pressure builds up very slowly. It blows all the time, straight out of the gun.
I have already replaced the two O rings, but without result. The wildcat can be filled, but with two steps forward and one back.