Overwashing does cause fog, but not instantly in most cases. If you go much over +50 mv in vAg during making, you are pretty much fogged, but if you do this during the wash, there is little immediate problem.
Underwashing causes crystals to form after drydown of the coating (unless it is a FB paper coating - many early paper emulsions were unwashed). Underwashing also slows down sensitization with sulfur or sulfur + gold. More heat and/or longer time will generally fix this problem.
Ferricyanide + bromide is a rather rare method used in this situation and can cause problems. I think that there is a patent on it by J. Hoppe of EK. The first version of Kodacolor 400 used a method similar to this for sensitization and fog supression. However, the oxidation process did something else as well. I am vague on the details as this was over 40 years ago that John Hoppe discussed this with me. So, I may be way off. If so, sorry.
The bottom line is to aim for 50 mv at the end of the was, or adjust to this point if you are more positive in vAg.