We've downloaded a demo site (Madrigal v.2) but when we try to add a project, a featured image can't be set. This results in projects not being visible on the page.

1. We upload a featured image
2. Then we press "update" button, the page reloads and the featured image disappears
3. The list of projects shows that all projects in the demo version have featured images (so they are visible on the website) but all the projects we add don't have featured images (so they are not visible on the website).

We know the required minimum width of an image and use slightly bigger images than the required minimum so this is not the source of the problem.
Please help us solve the problem.