Today, there was yet again an anti-semitic question on Stack Exchange, about Nazi Germany's actions against the Jews.
What do I mean by "yet again"? Well, in this Skeptics meta question from February this year, I noted that half of the "helpful" flags on questions on Skeptics.SE were about the holocaust, and approximately half of the remainder were about Jews or Nazi Germany. And the majority of the questions I flagged for holocaust denial were around for more than two hours, ranging from 6 minutes to 8 hours, 20 minutes.
And is it just Skeptics.SE? Nope, here's a quick sample from History.SE. One, two, three, four, five - and that's not going all the way back in my flag history. There have been some problematic content on Politics.SE, but usually it's less blatantly antisemitic, apart from this one.
I don't think it's a problem with diamond moderators. They've tended to do the right thing, and the fact that it happens on more than one site indicates it's probably not an issue with a particular moderator. I also believe that the smoke detector tries to deal with this.
I don't think it's an unsolvable problem - it seems to be the a very small handful of people or groups posting the same hateful garbage again and again every few months, for example compare Were Nazis favorable to zionism? and https://skeptics.stackexchange.com/questions/44757.
For the avoidance of doubt, I want Stack Exchange to act on all bigotry, and I've flagged on a variety of bigotries (people who are bigoted against Jews are also bigoted against other groups), but this is the particular ongoing problem I've faced in my experience as a non-diamond-moderator high-rep user.