Ah! You don't need to enter the exact number of comments in this field, you can leave it at 100.

Entering a max of "26" manually is what created the off-by-one error, I think, because of the original post being counted as a comment.

But yeah, I'll fix that.

If I leave the max at 100, then I get every comment (original post + al 26 comments), here's the output audio: https://drive.google.com/file/d/1fIis8yQn-YuOmJwq1J4cLtthQV0...

Update: I fixed it. The parent post is no longer counting towards the limit.