I know I've reported this before but without much to substantiate... Sometimes, haven't figured out if there's a pattern yet, I don't see a count of new items on the "bell" - but if I look at New Posts or even just click on the bell there are clearly unread items. I've stopped using Tapatalk so I don't think it's that. I know if you click on the bell once, then the count goes away (wondering why it wouldn't just decrease the count as some get read rather than go away altogether, but that's another issue), but I notice this when I haven't seen the unread count and get curious as to why since I'm subscribed to some active threads.
EDIT: Now that I look at that screen shot, these are fairly old posts. But New Posts shows newer items that don't show up like MOTD for example.