If you’re making an app for your event which highlights event location information, the event lineup, and allows you to plan where you’ll be throughout the day, it’s essential that you make sure this information remains available when there is no reliable internet connection.
Whether the convention centre has guaranteed wifi, or you’re relying on cellular service at an outdoor event, networks get saturated or have hiccups. Greeting your user with a screen like this completely undermines the effort of publishing an event app in the first place.
In other words, you need to offer an offline mode, or don’t bother. It’s a waste of everyone’s time when you force attendees to struggle with an internet connection when they’re trying to enjoy your event.