Discogs will not let me login with my own domain (of 30 years) and required one of the big providers. It kept complaining about "risky domain". But that is the only incident I can think of.
It is a top 1000 web site according to Alexa rankings. It would take you about 5 seconds to Google about it. Probably less time than it took you to write your post.
I have heard of that, yeah. It's still busted, but marginally more understandable if they're dealing with a lot of scams. For instance, `.xyz` and some others have bad reputations. I've never seen something that'll reject an arbitrary self-owned `.org`, by way of example.