Certain TV features and apps may not be supported by Multi-Link Screen. Multi-Link was mainly designed so that you can use an application such as the web browser or one of the other Smart apps while simultaneously viewing television.
I just picked up a UN65JS8500FXZA and was surprised with the multi link feature. The idea is great but my tv won't let me use it between the two HDMI sources. It worked once for me but hasn't again. Is the feature disabled on the TV with the two HDMI sources or is there a way around it?