ATEM Mini blanks out every hour or so

I have an ATEM mini which is switching HDMI video at 1080p/60 from a number of PCs and a Mac to a Philips HDMI monitor.
The input from the Mac Mini (via Thunderbolt->HDMI Adapter) blanks out every hour or so.
When it blanks out the Mac does not know. The only way to recover is to reboot the Atem or unplug/replug the HDMI Input. The monitor thinks it is getting a valid, but blank, signal.
I have spent a lot of time trying to get to the bottom of this, and have concluded it's probably an issue with the ATEM Mini because of the following:
1. Plugging the HDMI Adapater directly into the monitor = no issues.
2. Using another brand of good quality HDMI Siwtcher = no issues.
3. Using the cheapest 4-in, 2-out HDMI Switcher from Amazon = no issues.
4. Moving the Mac input to a different port on the Atem = same issue on all ports.
I have tried altering the framerate and the same thing happens on each setting.
So I think there is maybe something in the Atem firmware or hardware which doesn't quite like the input from this HDMI Adpater? After some time it just blanks the signal only a physical act will re-sync it.
My ATEM is running f/w version 8.6
*EDIT Spelling and Grammar *
The input from the Mac Mini (via Thunderbolt->HDMI Adapter) blanks out every hour or so.
When it blanks out the Mac does not know. The only way to recover is to reboot the Atem or unplug/replug the HDMI Input. The monitor thinks it is getting a valid, but blank, signal.
I have spent a lot of time trying to get to the bottom of this, and have concluded it's probably an issue with the ATEM Mini because of the following:
1. Plugging the HDMI Adapater directly into the monitor = no issues.
2. Using another brand of good quality HDMI Siwtcher = no issues.
3. Using the cheapest 4-in, 2-out HDMI Switcher from Amazon = no issues.
4. Moving the Mac input to a different port on the Atem = same issue on all ports.
I have tried altering the framerate and the same thing happens on each setting.
So I think there is maybe something in the Atem firmware or hardware which doesn't quite like the input from this HDMI Adpater? After some time it just blanks the signal only a physical act will re-sync it.
My ATEM is running f/w version 8.6
*EDIT Spelling and Grammar *