It's probably a location thing, or, since it is often fleeting - maybe an observation thing.
A most obvious demonstration of how wax moths work, around here: For instance, when growing 5-comb, medium, top bar nucs, with strong, Langstroth nucs, being converted -> wax moths often infest the bottom-most rows of capped brood, in the new combs. It escalates, to where the bees attack the wax moth larva, tearing out the infested comb, afterwards they rebuild the affected comb. If I weren't checking these hives, nearly every day, I would likely have never witnessed this -- it all plays out very quickly. Since I'm only able to apply Bt 'Aizawai' to idle combs, or new plastic or wax foundation (and I rarely use wax foundation), it's combs, unprotected by Bt, that seem most vulnerable, and hence, affected.