Proxies Unload and Delete Themselves

Suddenly, my proxies are unloaded. In the mini-map, everything is still loaded, so I cannot load the proxies there. Unloading everything/anything in the mini-map does nothing.

Show > Landscape remains checked as true.

If I close and reopen the project the proxies are gone.

Landscape Gone

Has anyone seen this issue? Any suggestions? All I can do is try and restore a backup.

If this occurs because there were too many levels/proxies loaded, then there should be an warning or error message.