SDI to HDMI Convertor with ATEM Mini Pro ISO

I am trying to use a Blackmagic Design Micro Converter SDI to HDMI 3G to connect my cameras to an ATEM Mini Pro ISO. I have plugged in 1 camera with the SDI converter into input 1, plus 2 cameras via HDMI cables into inputs 2 and 3 and PowerPoint via HDMI from laptop into input 4. This set up works, but if I try the SDI converter in any other input other than input 1, it doesn't work, ie. no video signal if I try to use the convertor on inputs 2,3 or 4.

I have my ATEM Mini Pro ISO set up video standard as Auto. All my cameras are 1080p, either 25 or 50 fps (UK). Changing to setting it manually doesn't make any difference.

I have also an email directly to BMD support about this but asking here too in case anyone else has experienced this.

How long is the HDMI cable between the converter and the ATEM? HDMI 1 has a different interface chip than the other three inputs which is more forgiving to sub-par input signals.

How long is the HDMI cable between the converter and the ATEM? HDMI 1 has a different interface chip than the other three inputs which is more forgiving to sub-par input signals.

I have tried varying lengths - a few centimetres to much longer.