Featured Image Missing

The box for featured image appears to have vanished from the right menu on page/post and any plugin that has a page interface. It is also not listed as an option in the Screen Options.

If I switch off of Switty to the default WordPress themes, it returns.

It was there originally, we designed the site using it, and the images are still there we selected in the past, but we cannot add more or make changes unless we switch themes, make changes, and switch back.

The page I need help with: [log in to see the link]