Recent release changed Sandbox functionality?

Summary

Trying to understand how the sandbox functionality has changed since 19c.

Content

Hello all!

We are working to prepare for the HCM and other UI changes coming soon in 20a and 20b. Unfortuntely we do not have a great understanding about what personalizations have been completed in our environment, and we're working with Oracle to help get a report to tell us what we've changed. 

While we work that front, we also need to better understand how the sandbox functionality has changed since 19c. In our recent upgrade to 19d, we now no longer see all the sandboxes we had previously published. If, for example, we had a field hidden for a specific page, we no longer see the sandbox which we had used to publish that change.