Dev Kit - Everything missing in Scene Outliner & Preview

Since today, whenever I open any map, other than the testmap, it comes up more or less empty. I can see the sky and a few trigger boxes, other than that its gone. However if I press play, everything shows up just as it should and the Scene Outliner finds 1000s of actors. Once I get out of Play and back into the regular mode, its all gone again. Nothing seems to be hidden, the preview window is lit and has everything else enabled as usual.

Image of the error:

You need to enable the other sublevels from the Windows/Levels menu. Although I don’t know why you’d want to.

That did it! Thank you so much.