I'm so sorry to hear that your students have lost their presentations or run into issues where they're not saved properly!
There are a number of things that can contribute to this happening, including outdated versions of the iPad app being used, and decks not being saved by exiting edit mode. The best way to prevent this is to have students follow the steps here.
Here are the steps that students should follow to have the most reliable experience possible with sharing the iPad app:
1. When you pick up an iPad to use it, make sure that Haiku Deck is signed out of someone else's account. If the button in the bottom left corner of the Main Menu says 'SIGN IN,' you're in the clear - otherwise, tap ACCOUNT and then tap SIGN OUT. Do not tap ACCOUNT and change the email address in the popup.
2. Tap SIGN IN in the bottom left, and sign into your account.
3. When you are finished working, save your work to the web by returning to the Main Menu with the button in the top left corner of edit mode. Even if your deck is private, this ensures your project is stored in its current state where you can pull it up on any iPad later, or on the web.
4. Tap ACCOUNT in the bottom left.
5. Tap SIGN OUT in the window that pops up.