In reviewing the code for the Blackmagic nodes, we found a piece that might cause video mixups like you demonstrated. This could happen when using 2 or more Receive Blackmagic Video nodes. We'll have a possible fix for you to try in the Vuo 2.0 beta.
Thanks for reporting this problem and taking the time to test various configurations.
On an extremely complex composition that I can't unfortunatly post I couldn't get 2 Receive Blackmagic Video nodes using 2 Blackmagic UltraStudio Mini Recorders to work in the same composition properly. Watch link below to see an example of the issue. Each BM UltraStudio Mini Recorder has it's own address and can be used in OBS together and usually worked in a much simpler Vuo composition but has issues in the complex composition. What's even stranger is that swapping the BM node out of the receive live video node fixes the issue with nothing else changed so this has to be an issue with the BM node itself I think. Right?
I have tried to create a simpler composition showing the issue but only ran across the issue one other time. However after a reload of that project it started working properly and I wasn't able to recreate the issue on that project again.
Have you found a workaround?:
Make sure you are using MacOS 10.14.3 or earlier. With nothing else changed I replaced one of the Receive Blackmagic Video nodes for a Receive Live Video node and this resolved the issue.