I just read this blog post about "tribe gaslighting" and was kind of astounded because this EXACT thing has happened to me multiple times:
https://www.psychologytoday.com/us/blog/guide-better-relationships/201811/gaslighting-tribe
Basically she is just talking about how groups will often gaslight on behalf of a narcissist, by refusing to acknowledge another person's experience with the narcissist. So they'll say things like "Oh, that's not my experience with her" or "I've never noticed him acting that way" instead of listening to what someone is saying.
I was in a workplace a few years back and this is exactly what happened. Our boss was incredibly inappropriate and boundary-violating with me. Stuff like: commenting on my personal life in the middle of staff meetings, criticizing my eating habits, making comments about how my clothes fit or how I wore my hair. Whenever I would bring it up with anyone else at work, they'd kind of shrug and say that they had never noticed it or that they didn't think that stuff was a big deal. It made me feel crazy and after I left that job I spent a lot of time thinking that I was the problem, that I was too sensitive and needed to get over stuff like this.
But this is what it was: tribe gaslighting. That boss was super inappropriate and probably should have been fired or, at a minimum, sent to an extensive training program to address this behavior. I can't believe I ever accepted any of it as normal.
Anyway, passing this along in case other people go through this. I wish I'd read this exact article years ago so that I would have understood what was going on and had a way of talking about it.