We should describe, that once app receives the event without error in the handler, WalletKit considers it delivered. Callback for that event shouldn't be triggered again(But in some cases it can fire more than once, if some error occurs during updating state of the event)
That means that you should

• Store events durably after they are received, so user won't lose them after reload of the tab for example
• Do not show same event to the user more than once