All my suppliers have disappeared. If I try to add a supplier that was there it says it can't be added as it already exists?

Hi matthew-ely13, thanks for joining the Community

We don't have any reported issues with accessing or creating suppliers in QuickBooks Online at the moment. 

To check for any browser issues that may be impacting this, please try signing in using a different web browser or incognito window. If you're able to access your suppliers as usual there, consider clearing the cache and cookies so that you can continue using QuickBooks in your regular browser. 

If using the app, please fully uninstall and reinstall this to the latest version available in your app store.