I had a similar thing with a friend I was pretty close with, I said something that he didn't like in a group chat we had, not even very insulting from what I remember, but he never told me, or anyone else.

I showed up at a party and he was just not talking to me and wouldn't say why, his GF didn't know anything about it, no one in our chat who I asked could point to anything I said that could possibly cause the reaction.

Eventually he just started talking to me again, never mentioned anything about it. Then he did it again, once again IDK what I did and no one else does either.

I can't say I did nothing wrong because...idk what he was upset about and you can't apologize for some shit that you don't know what you're even doing it for.

But from my perspective, it's not sustainable to be friends with someone who communicates in such a way.

There are a few things I needed and need to learn to Let go, but at the same time, there are people who I can't see as having changed enough that I would let them back to being close again because the same shit would repeat.