> Anecdotally, in the startup where I worked there was one summer in 2017 when 3 white women (a significant percent of the women in the office at the time) all suddenly came out as non-binary and asked to be called they/them. If that's not some kind of freaky bandwagon thing going on then I don't know what is.

Have you considered that they may have been talking about it privately, and decided to come out at the same time to reduce the risk of being singled out for it? I don't see how the timing implies a "bandwagon". It seems obvious that doing that together is less scary than alone.