I'm also experiencing something like this. Some comments are syncing, after a little while, but not very many. Some insight into how commenting syncing works and maybe how we can configure an instance to be better at it would be nice. Viewing this same post on lemmy.ml, I can see there have been several comments, but viewing the post while logged in to my own instance there are currently none visible.
I am pretty sure it's not an issue of language settings, in my case, since the posts that comments have synced for show comments tagged with English and also comments with no language tag.