I had exactly the same result from my first batch of Pyrocat-HD, but right from the start. At the time, I put it down to bad phenidone, since the other chemicals have proved since then to be ok. I don't believe that I made a mistake in mixing.
I need to make the following admission to not following the instructions completely. I made up a stock solution of 5gram phenidone in 100mL of alcohol (95% food grade). I used the appropriate amount of that stock solution
My next batch was using metol (at Sandy's recommended amount) instead of phenidone since I was worried about my source of phenidone. I have been absolutely delighted with the metol version, and I get at least EI 320 out of Neopan 400, which is fast enough. Probably a bit more with minimal agitation.