This question has been answered by sottwell. See the first response.
Are they still in the site_htmlsnippets table in the database? Could that table possibly have become corrupted and need repair? Have you been doing anything with the ACL permission system?
Are they still in the site_htmlsnippets table in the database? Could that table possibly have become corrupted and need repair?
If a table is already OK, the repair operation won't affect it. I've never had repair cause a problem.
If you're nervous, you can always create a backup first using the "Export" tab at the top. It's not a bad idea to do that anyway whenever you're messing around in the database.