Wordpress site missing

I'm sorry to hear about the issue with your WordPress site. This can be a frustrating situation, but there are several steps you can take to troubleshoot and potentially recover your site.

1. Check your Lightsail instance: Since you mentioned restarting the instance, it seems you're using AWS Lightsail. Ensure that the instance is indeed running and that there are no obvious issues with its status.

2. Review recent changes: Although you mentioned not making changes since yesterday morning, it's worth double-checking if any automatic updates or scheduled tasks might have occurred.

3. Check for automatic backups: If you have enabled automatic snapshots in Lightsail, you might be able to create a new instance from a recent backup. This could help you recover your site to a working state from a few days ago.

4. Database restoration: If the issue is related to the database, and you have configured automatic backups for the database on the host, you might be able to restore it.

5. Use WPVivid plugin: You mentioned having a backup of the site. If you have the WPVivid backup restore plugin installed and enabled, you might be able to use it to restore your site. However, this would require access to the WordPress admin interface, which you mentioned is currently unavailable.

6. Check server logs: If you have access to the server logs, review them for any error messages that might indicate the cause of the problem.

7. Disable plugins: If you can access the file system of your instance, you might try renaming the plugins folder to disable all plugins. This can sometimes resolve issues if a plugin is causing conflicts.

If these steps don't resolve the issue, you may need to consider more advanced troubleshooting or potentially restoring from your backup to a new instance. If the problem persists, it might be worth contacting AWS support for further assistance, especially if you suspect it's an issue with the AWS infrastructure rather than your WordPress installation.
Sources
Recover wordpress version | AWS re:Post
Appendix C: Backup and recovery - Best Practices for WordPress on AWS

Ive seen this before with Wordpress not related to AWS where I updated PHP before without updating the plugins first.

Do you have auto updates enabled?

Hi, please check following things 1)Recently if you have installed any plugin or put auto update. Try to login via ftp and remove that plugin manually

2)Check your WordPress database connection

Thanks