[noggin]

Now I tested my Mecool M8S Pro, Amlogic S912, running the latest version of CoreELEC, and same thing.  The refresh rate was already set to start/stop.  

So, I have tested on 2 different TVs, one HD and one UHD.

Tried 2 different Windows 10 microPCs, running Kodi 16, on two different TV's.
Tried, my new, Mecool KM8 (Amlogic S905x), with both Android Kodi AND LibreELEC (BTW Wrxtasy's remote config make the stock remote work).
Tried Mecool M8S pro L (Amlogic S912),  using Android Kodi.
Tried Mecool M8S Pro (Amlogic S912) running CoreELEC.
Tried Xiaomi Mibox on 2nd HD (1080p) TV, with setting start/stop..... Same thing 1080p/60
Tried Zidoo X9S, Android Kodi and their player, still 1080p/60

Perhaps I have just entered into the Twilight Zone........

I can't think of anything that might be causing the issue with your setup. Are you connecting these boxes directly to the TV or is it being routed via your AVR? I understand from one of your posts that you have an older AVR, not sure whether that could be the culprit here. 

Could the OP be running Leia without setting whitelist resolutions and frame rates?