VPX: LG Video Wall, loss of video

This was a scenario using LG Video wall monitors which have integrated video wall processing. 

ISSUE: The HDMI gets daisy chained from one monitor to the next and each monitor knows its position in the wall. It was being fed by a single VPX decoder. Very frequently the last 3-5 monitors in the chain would flicker and sometimes go completely black. 

SOLUTION: The problem was that Genlock was enabled on the decoder. If Genlock is not locked to a reference, the video output can contain a small amount of jitter. The video wall apparently does not re-clock the video each time it is daisy chained and thus causes jitter accumulation on each hop. The was enough to cause loss video at the end of the daisy chain.