At my church we have a display system that uses a HDMI splitter to drive three 1080 TVs as well as an old (might be relevant) 1080 monitor. We were running this setup off a 2012 MacBook pro with a Thunderbolt to HDMI adapter with no issues. On the MacBook pro the external display setup was recognized as a TV, and I was able to select 1080p from the list of resolutions, which worked properly.
We just upgraded to a new MacMini with the built in HDMI port. Unfortunately, when I plug the HDMI cable going to the splitter into the HDMI port (along with a separate monitor connected to one of the USB-C ports), the external displays don't work, showing an out-of-range error indicating a bad resolution. What it looks like is that the new computer is recognizing the splitter as a 4K display.
To try to work around this, I got SwitchResX and set it to one of the 1080p60Hz options, which seems to match what the old computer was outputting. Unfortunately that only worked for the large TV displays - the old, small, monitor is still showing "bad resolution" messages, and while it does display an image, it is incredibly distorted (color issues).
Is there a way I can get my new MacMini to output over the HDMI the exact same way the old MacBook pro was outputting over the thunderbolt->HDMI adapter? Or, since the output IS working for the TV's, is it likely that replacing the monitor would fix the issue?