1) If the resolution of your input source (like computer/ laptop) is higher than the resolution of output devices, it won't display normally. For example, your computer is 1080P, but both 2 TVs are 720P, then the displays will not show up. In this situation, you need to set the resolution of computer to a minimum, until the TVs have images, then slowly increase the resolution of the computer until the images on the two TVs are clear.
2) If the resolution of your output devices have different resolution, it won't work.For example, your laptop is 1080p, one TV is 1080p, the other is 4K. Then you need keep same resolution on 2 TVS, that's to say, your 4K TV need be adjusted to 1080P.
Input device resolution setting method: Application -- Settings -- Display -- TV resolution -- Suitable resolution