How to fix this FB Messenger Problem, or is there is?

So here's the story… Whenever I send a message to a a specific person that I want to chat with a circle and a check is showed sow it ses that it is sent but never delivered why is that… I know people said that unless they checked out the chat on messenger then it will be delivered but… Why is that ow yah I'm on a mobile device by the way… ( Asus Zenfone 2 ) it also happens on my ipad and freaking pc… Usually right that if you sent a message to someone even though their offline it will be delivered and a notification will pop out on there device but why is it not doing like it supposed to do last time wth!

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