API call GetComments sometimes returns no comments

This happens for me on a small number of posts, and is generally repeatable, even when the website shows comments.

For instance, running on lemmy.world, GetPost(id: 290602) tells me the post exists and has 7 comments, as does https://lemmy.world/post/290602

But GetComments(postId: 290602) returns an empty list.

If I run against the original post on 'programming.dev', GetComments(postId: 99912) does show me the comments, but I don't think I'm supposed to be second guessing the federating logic :-)

Has anyone seen anything similar or can confirm they see this same behaviour for this post?