It could be a bug, but let's start by telling us the version of ID (and the patch number) and your OS.
Is this a Book (.indb with a clooection of individual .indd files) or a single document?
It's actually not a "book," just a single .indd file. I'm using ID 18.104.22.168 on Windows 7 (I know, but it's my work comp). This started happening after a particular edit, but I couldn't tell you what action caused it - I'd been adding and editing tables, probably copying tables and pasting in new data, etc. This doc is all tables btw, and the items that should be showing up in the TOC are the table headers, all of which have the same paragraph style applied. I've even tried applying a different style and the re-applying the TOC style - it just absolutely refuses to add certain headers to the generated TOC. Looking in the Story Editor, which I've never hitherto used, right now to see if I can figure anything out...
Nothing wrong with Win 7 (my personal OS of Choice).
This seems highly unlikely in your case, but check to be sure that you don't have multiple styles with the same name in style groups or with different capitalization. You might want to try this, too: Remove minor corruption by exporting
Ya know what - I had a deadline and it was a short price book, so I just entered the missing entries manually - but then I had to create a new version with just a few edits, and ran into the same issue of course, so I tried exporting to idml and reopened it, and sure enough, the TOC works now. Something got corrupted somewhere. Anyway thanks - that definitely solved the problem.