Messages disappear before I can even read them

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Level 1
I’m not sure if this has happened to you but there have been several times where I get an alert for OfferUp saying I have a new message. So I open up the app, I see that there is an icon stating how many messages I have, however when I click on the message icon there are no messages. I get a statement saying no new alerts/messages available. I have already deleted the app, updated the app, and even logged out of my profile and I still get the same result. Any ideas why these private messages disappear before I can even read them?