Perhaps not all HDMI's are created equal?

At my church, we have been using Blackmagic Design ATEM 1 M/E Switcher to receive two camera inputs and an audio mix input. Its HDMI output was split into two, where one went to a TV, and the other was converted by VECOAX Micromod 3 and sent to another TV using a coaxial cable.

Recently, the ATEM switcher decided to die, and we are trying to connect the camera inputs directly to vMix (using Decklink), and send output HDMI to the same TVs mentioned above. To our disappointment, the first TV refused to accept the the HDMI signal, complaining about unrecognized HDMI signal. The 2nd TV (connected via coaxial cable) displays the video fine, but the audio is choppy.

That said, iI'm wondering if there is a way to modify vMix's output HDMI signal so that these issues can be resolved.