There is a problem with either wattbot or the app, I've seen a few posts with the same issue and it also happened to me yesterday.
I sent a message to the team and received a message (not in the app) to say I had a reply. When I clicked on the message it took me to a blank wattbot. I then sent another wattbot message (that may well be irrelevant- I don't know) to say I couldn't see the reply. When I opened wattbot later on there was a reply. Clearly this sort of behaviour is going to cause and is causing huge frustration for customers.
I'm perfectly happy with the response to my request (I asked to change the DD amount), but this is not the first time stuff has disappeared from wattbot (and I was logged in).