UPDATE: Experimented and tried scrolling up to the top of the particular message and "pulled down" to cause a refresh. At least in one case, the messages for one account refreshed, and the missed messages appeared.
So... PLEASE look into whether messages need to be sync'd more reliably.
Getting Android app notifications for messages but they don't show in the app. I uninstall then reinstall, which clears the problem for a day or so, then the same problem starts again.
Messages in browser are fine.