Why are my cameras in sud stream?

[electricblue]

In main stream I only had one cam in live view. Finally I found by clicking sub stream the other cams came on in live view. Why are they running in sud stream?

 

[alastairstevenson]

Why are they running in sud stream?

That's the default in multi-view.
Just as main stream is the default in single view.
Likely the NVR isn't able to decode all main streams in multi-view. What do the specs say?