On the large format forum there has also been some discussion on it. Or perhaps that was only about unexpectedly low activity of ready-bought pyrocat. I can't comment; I haven't experienced it myself with my DIY chemistry. The formula doesn't seem very prone to sudden death looking at its chemistry; perhaps the vitamin C versions are more likely to exhibit this, analogous to XTOL.
I lied. That was the only time I've heard of this issue. Mix from scratch is the safe option.
