Delete and re-install the app. Facebook Messenger does the same occasionally for me, seems an app issue rather than iOS though...
Will I lose all my contacts and data if I delete and reinstall the app?
If you restart the phone it usually fixes this iOS 10 bug
It seems that this isn't a widespread issue, although some are having it. You might want to try resetting all settings to see if that gets it working properly, or perhaps even reinstalling.This is a huge BUG issue for me, I've missed Whatsapp, email, FB notifications at random. Contacts had to reach out to me via Phone due to this issue, which makes me reboot my iPhone 7 every week. Also once in a while REMINDERS also get stuck in a sound loop notification (almost like a Rave DJ!).
This is getting very annoying, fix iOS 10 !
It seems that this isn't a widespread issue, although some are having it. You might want to try resetting all settings to see if that gets it working properly, or perhaps even reinstalling.
It's software, weird install things can happen, and as we see in all kinds of posts do happen. It doesn't mean that it's very common or that they should or that it's good or anything like that, but it's not all that unusual. And when it does there are some troubleshooting steps that can be taken that at least sometimes if not often can resolve some of these types of things. Can be a pain, sure, but I guess the alternative is to live with the issues.Email & Reminders too ? Come on now, this is too silly ... Never had any issues on my 6 Plus on iOS 9.x.x