Cool! Yeah I’ve heard of that one. Was that the one everyone was banning a week or two ago, and they were all upset about it?

Nah, lemmygrad.ml has been around for years, is run by the founding devs of Lemmy, and is part of the reason some people refuse to use Lemmy (especially if their reasoning is the devs). You'll find quite a few people with that viewpoint on Kbin.

When browsing that list, one of the top ones by users was Lemmy NSFW, but I’ve never seen a post labeled NSFW on my All feed, and I just checked both apps I’ve used (Jerboa and Liftoff) and they both have show NSFW enabled. Is that filtered or do they just have a lot of users and nothing gets posted up promoted enough to be seen? I’ve seen stuff from most of the other top instances fairly frequently.

When I go to the All feed right now, and choose "Top Twelve Hours", I see one from that instance on the first page. However, it only has 85 upvotes compared to the hundreds for the top posts so maybe they struggle to get visibility.

By the way, for those interested, here’s what I was looking at: https://github.com/maltfield/awesome-lemmy-instances

In case you're interested, the instances blocking hundreds of other instances are likely doing one of two things.

1. Blocking instances with thousands of user accounts and a small number of active users - there has been a spam bot boom the last week or so. These instances are often genuine but the default lemmy settings make it easy for bots to sign up. Even here I had one overnight period with 8,000 bots signing up, then I spent a while playing with settings so that we could have open registrations (they were closed for a couple of days in the last week trying to get it sorted.
2. Some instances are finding that failed attempts to contact other instances can lead to performance problems. e.g. if an instance used to exist and someone from that instance subscribed to a community, then your instance will keep trying to push new posts to them (and try again if it failed). So I have seen some starting to block lots of instances that used to exist and no longer do so that Lemmy doesn't keep trying.

Both of these are likely to become an issue for us at some point, but we seem to be small enough and flying under the radar enough that neither have required too much action.

BTW I just learnt that all instances have a /instances page that tells you who the site is federated with, and also who the site has blocked. Here's ours: https://lemmy.nz/instances