Hi Stefan, Pyrocat will typically tolerate anything from contiuuous agitation to virtually no agitatiion at all.
It sounds to me like your developer got very oxidized somehow. Maybe your developer temperature went way high - - that could do it.
Diluted Pyrocat - ready to use -should be a very pale pink or peach color. What color was the working developer just after mixing it?
The color after development may not change much, or may shift to a yellow or amber color, depending on the film type.
The only time I've seen it go brown is when I mixed it with water that contained a very heavy load of dissolved oxygen.