ATEM Mini Pro ISO - HDMI Output

I'm using an ATEM Mini Pro ISO. I need to output to 2 monitors. I have tried several HDMI splitters. None of them work. Outputting to each monitor individually, everything works well. As soon as I plug everything into a splitter, I get nothing on either monitor. Each monitor recognizes that it has been plugged into something, but the screen remains blank. This is the case for all of the output selections(Camera 1, Camera 2, Camera 3, Camera 4, Multiview, Program, and Preview) but one. It does work if I select "Camera 1 Direct". Does anyone have any idea why this might be?

I’m using these cheap Delock HDMI splitters and they work great. And they don’t need external power.