Hello!
I have an odd one. On a client site, I can send details in a private note, we have custom headers, footer, and blocks, yet when I go into edit them it says there are not and to create one. Again, we can see them displaying just cannot get to them in the admin.
Side note, we have not yet updated to WP 5.7 as the website uses a lot of gravity from and it appears there is a rendering issue on 5.7 and the Latest Pro, so we held off.