I run two identical monitors that are AOC Q27G3XMN with Windows 11 and a GeForce RTX 4070 Super. Monitor 1 on the left, I use as the main monitor with the taskbar and mainly to play World of Tanks and Monitor 2 just to watch youtube etc. Both monitors have the same set up.
 
I initially noticed that monitor 1 would revert from RGB to YCbCr422 (Limited) upon a start up and not allow me to change it to back to RGB. Monitor 2 would always remain on RGB . At first if i removed and repalced the DP cable on monitor 1 it would allow me to select RGB but again revert to YCbCr422 the following day when restarted.
 
After seeing a post on here from a few years back, although way out of my knowledge range I reduced the monitors refresh rate from 180Hz to 170Hz. This did sort of work and both monitors would stay on RGB. It then became apparent that although monitor 2 would always stay on RGB 10bpc, monitor 1 only offered 8 bpc. I thought it was a DP cable issue so now both have the same cable as monitor 2 that always works fine (Silkland Vesa Certified Displayport Cable 2.1/2.0 2M, DP Cable Supports 4K@144Hz /165Hz /240Hz, 8K/10K/16K@60Hz, 40Gbps, HDR, ARC, DSC 1.2, G-Sync & Free-Sync, DP 2.1 for Gaming Monitor, Graphics Card).
 
Monitor 1 will now hold on RGB but only offers 8 bpc where as monitor 2 still holds on RGB with 10 bpc. If i revert the monitors back to 180Hz refresh rate, again monitor 1 flicks to YCbC2422 and monitor 2 untouched. If i select RGB for monitor 1 and click apply it just bounces back to YCbCr422. Until i select 170hz when monitor 1 again gets RGB 8 bpc and monitor 2 RGB 10 bpc
 
I cannot fathom why the two identical monitors act differently like this being the same, with the same settings?

Did you try using the same DP output port and same cable that works on the one monitor on the other monitor to see if the problem follows?

If it the issue stays with the monitor, it could be the monitor. If the problem swaps, then it sounds like it could be a cable issue, or a driver / windows issue.

Hello arestavo,
 
So should I just swap the DP cable from the back of the monitors over and test like that?

Gareth2665
Hello arestavo,
 
So should I just swap the DP cable from the back of the monitors over and test like that?

Yes, just move DP cable between the two monitors / not GPU ports.   Your testing if it is a monitor issue or a cable / Windows, driver issue
 
If nothing else changes & M1 still does not work as expected ... check monitor firmware & other settings are the same between both monitors
 
Also, try turning Off deep sleep, if your monitor has that option

Arestavo & Cool GTX,
 
Than you kindly for your inputs as the problem now appears fixed. No clue how so assuming it was a fluke or a Gremlin somewhere.
 
I did swap the DP cables over as suggested but had same problem. Both offered, and stayed on 10 bpc until i restarted the PC where Monitor 1 again only offered 8 bpc.
 
However It does now stay with both on 10 bpc. The only change I think, is that i now turn off both monitors with their power buttons when shutting the PC down and turned off the "Sleep Mode" on both monitors. . Before i just left them in standby and the Monitor Sleep mode was on.
 
Not sure why this may of helped as I would of assumed what ever change this made, ie reducing bpc to 8 on Monitor 1 would effect both monitors.
 
The only difference is Monitor 1 is the Main Display.
 
I would like again to thank you both for your help. Without people like you and Forums like this many of us "Less Technical" people would be pulling our hair out with these problems that occur.

Good to see it is working correctly for you
 
I also should have mentioned; clear your Windows startup File - to make Windows Look for hardware & Software changes to your PC on the next startup
 
To clear your Windows startup File --->>> hold shift key down, (keep it down till All Power if Off to PC) now select shutdown from Windows menue)
 
 
Happy to Help 

Cool GTX
Good to see it is working correctly for you
 
I also should have mentioned; clear your Windows startup File - to make Windows Look for hardware & Software changes to your PC on the next startup
 
To clear your Windows startup File --->>> hold shift key down, (keep it down till All Power if Off to PC) now select shutdown from Windows menue)
 
 
Happy to Help 

Cool GTX,
 
I have stumbled upon the actual problem now. As I said before it is down to how the Monitors turn on and on two occasions now, Monitor 1 has turned on when booting the PC rather than me pressing the power button.
 
On both these times, Monitor 1 reverted to 8bpc. If i had to turn both Monitors on with power button both set at 10bpc.
 
All I did was just turn Monitor 1 off and back on with the power button. When it goes off the main screen bounces over to Monitor 2 then as Monitor 1 comes back in it switches back and sets at 10bpc.
 
I have not cleared the Windows start up file as I didnt want to bugger it up now it seems ok. Should i still do this?

Yes, it is a basic way to help/Make Windows "see" any system changes.
 
Otherwise, Windows uses the file from the last successful startup & Ignores any system updates or changes
 
Any time you change Drivers or Hardware.
 
I disable Windows Fast Startup or clear it, on my own Rigs --- yes, it takes a few more seconds for Windows to start; but, the info is up to date