No items visible in backend

Hello,
In the backend we can not see any items or saved layouts anymore.
Visual Portfolio is telling us there are no (zero) items and layouts.

However, on the frontend there is no problem, everything works fine. Portfolios are embedded with shortcodes.

Plugins disabled or a default theme does not solve this issue.

Hope you can help.

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