Why isn't my Facebook chat on iPhone working?

I do all the app updates from the App Store for all my aps including Facebook on my iPhone 5. Recently I've noticed it doesn't show the actual online people, just favorites and then the people who are on mobile. But occasionally a green dot or two. A few times the green dot actual online section comes back but it shows a very very small amount of people online even during the peak hours which I know is incorrect. Also the people who are online by phone or mobile has stayed at the same constant number. Is this a glitch or how do I fix it?

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