It’s not just lemmy.world. Sample: https://lemmy.ml/post/1291098 (yes, someone else posted the song later, but this one isn’t showing from here, at least not for me)

Noticed it in other communities too, some posts are randomly missing. But also some comments are sometimes missing from posts. Look here, different community from a different instance:

https://lemmy.ml/post/1288661 (5 comments, one deleted)

vs

https://sopuli.xyz/post/727311 (one comment)

Hopefully it gets fixed, in the meantime I’m switching between instances a wee.

Not sure how popular this is but The World Is Quiet Here got a whole lot of eartime from me with their last album Zon.