I'd be happy to help you. It looks like you have the two computers from us-- just to clarify, are those for two different locations? I was wanting to verify so I can make sure your license is organized correctly to avoid confusion.
Which computer are you having the issue with by the way? I'm not sure what resolution you are running at on the 4k TV, but I would say you need to set it to 1280x720 for best performance and if not, 1920x1080 will look great and perform more solid as well. I'm thinking the resolution if at 2560x720 + would cause the issues. So make sure to set those in Windows to 1920x1080 for the output screen and then equal that out in the Cue Setup in the Mediashout settings, then try again. Use the "resize the cues" setting, and then repaginate the cues before firing to test (from the file menu).