Sounds like the data stream to the LEDs is getting flakey. This could be due to a bad / loose connection, noise getting in the line, or excessive cable length. I suspect these are pretty close together so it's probably not a cable length issue. I suggest inspecting / wriggling the RGBpx cable and connections between kryographics #1 and #2. If it looks good, try going HighFlow NEXT -> kryographics #2 -> kryographics #1 and see if the problem moves with the block or stays at the end of the line.