What was the temperature of the ferment, what stage are you in and was it a vial/smackpack and when was the yeast packaged date?
Did you do a shubo method moto or 2-3 week natural build up? The acid might not be high enough stunting the yeast a bit.
Did you use the same koji on all 4?
I don't think too much is a problem. Is any of the yeast in a different batch? Did you rinse out the container well before starting? Did you put anything into the batch that might stunt yeast? Was the container previously used in a process that had either stunted/stopped yeast before?
I would re-pitch, especially if you used all the yeast from a single source, could simply be for whatever reason the yeast was DOA. What color was the yeast when you pitched? Dark peanut butter? That would suspiciously indicate bad yeast.
I don't think you can overpitch with a few vials/packs (add 5 or so, then maybe)... The moto is supposed to build the colony sufficiently anyway.
Let me know what you think.