I can see lemmy.ml threads, but they have 0 comments. On latest stable lemmy instances, not really seeing any errors in logs. It's possible I don't understand lemmy and comments aren't federated automatically? Welp, let's see if I can post from my instance to lemmy.ml at least.
Both Mastodon and Lemmy have this problem. Make the default where the most new content is, which is going to be the federated tab and all tabs respectively.