Under some circumstances, the app will freeze, especially when picking a winner. This sometimes happens if it takes us longer than normal to find a valid winner that meets all of your entry criteria.
If this happens, just force close and reopen the app. Then, you should be able to find your giveaway in the past giveaways tab with a winner chosen unless your giveaway is still active.
If you continue to have issues after closing and reopening the app, please get in touch with support so we can help.