Best guess: There was something in the post that the system saw as a possible violation of site standards.
In the previous community site, that sort of post was greyed out and marked as "Reported." But it was still visible. It would be "released" if the staff person who reviewed it realized that the post was acceptable. If it was unacceptable, it was deleted.
I can't say for sure, but the new site might move flagged posts to an area that's only accessible by staff. If that's the case, it should reappear after it's been reviewed by a human.