Hi Sven,
Were you able to troubleshoot this and/or did you replace this system with no issue?
Just reading over your posts, considering there was no flicker on the videohub monitor, did you ever try a different SDI to HDMI adapter on the receiver end?
I’m researching/consulting for a very similar use case and was leaning towards an SDI/videohub solution. I am surprised and confused to hear there could somehow be a protective measure sent through the analog output of the boxes…