Hi @Molly Simpson and welcome to the Community!

I used Miro and created a diagram yesterday on my work laptop. 

Are you using the same laptop today? If so, have you tried clearing your browser’s cache and cookies?

If you are not using the same computer/browser, are you using a supported browser?

If you are using the Miro desktop app, have you tried resetting the app data?

Are you connecting from a different network today, e.g., home vs an office?