Multicam-sequence suddenly doesn't show all cameras

[Victor281645274467]

Hello everyone, 

All of a sudden, my multi-cam sequence doesn't work properly. It only shows one camera angle even though all angles are turned on in the nest. However, what's also odd is that the "nest" doesn't seem to work properly, neither. I should be able to double-click the nested multicam-sequence and thereby open the multicam-seq in Timeline, right? I can't. In the pictures I attached, I opened the multicam-seq by right-clicking it in the Project Panel and pressed "Open in Timeline". 
Any idea what might be wrong? It's highly frustrating! 

Hope you can help. Victor