Forget about that, that won’t help after all.
I’d create a new post in which I’d paste the same markdown content as one of the unformatted posts.
I’d expect the new post to be properly formatted by Discourse.
Then, I’d compare the raw field of both posts; either with data explorer or the rails console.
If one is formatted when cooked, and the other one isn’t when you rebuild HTML (which rebakes the post), there should be a difference in their raw. 