Can switch display from Mac to Windows but not back

[JustinCEO]

Mac version: 10.15.6.
AMD Radeon R9 M395X 4 GB GPU, ran the installer with the appropriate parameter.
27" 2015 iMac with two external displays.
Window machine is running Windows 10 Pro with a GeForce 1080 Ti.

One external monitor on mac is an LG 32GK850F-B 32" Class QHD HDR FreeSync Gaming Monitor

That is the one i am trying to use with ddcctl.
I have the monitor connected through the monitor's single available Displayport connection to my Mac and through the monitor's HDMI 1 to a PC.
My 1440p LG is display 2 for ddcctl purposes. So I can run
ddcctl -d 2 -i 17
and that switches the display at issue from the mac DP connection to the PC HDMI connection.
alas, if, after doing that, i try to run
ddcctl -d 2 -i 15
to switch back to Mac, nothing happens.
Notably, after initially running ddcctl to switch to HDMI/PC, if I use my monitor's hardware input controls, the input selector is still set to DisplayPort,
AND if I just re-select DisplayPort using the hardware monitor controls, it does not switch, and the monitor has a graphical indicator pop up on screen indicating that the input is
now displayport. I have to switch to HDMI (which I am, in fact, already on), and THEN switch to DisplayPort, in order to get back to my Mac/DP input.

What about if i run
ddcctl -d 2 -i 15
after having first manually switched to HDMI/PC using the hardware monitor controls? Nothing happens, though in that case, after running the
ineffectual ddcctl command, the input setting on the monitor correctly indicates that the display input is HDMI (unlike in the previous case, where it was on
HDMI but incorrectly displayed DisplayPort)

Also, just as potential troubleshooting info, if I run
ddcctl -d 2 -i 15
when I'm already on the Mac/DisplayPort connection, the screen just blanks/refreshes for a second and then continues displaying as normal,
which is what I would expect if the command is being received properly by the monitor. So it does seem to work fine from the Mac end.

So summarizing:

1. I can switch from Mac/DP to PC/HDMI using ddcctl.
2. I cannot switch back from PC/HDMI to Mac/DP, regardless of whether I i) initially switched over from Mac/DP using ddcctl, or ii) switched over to HDMI using the hardware monitor controls. There is a variance in how the monitor reports its display input source after using these two methods, however, as described above.

[gherlein]

It's not clear to me: when you run the command to switch back to the mac from the PC, are you running that on the mac or on the PC?

[JustinCEO]

Trying to run it on the Mac. Is that an error?

[gherlein]

I'll defer the answer to that to some of the experts here, but on my rig my monitors only listen to DDC commands on the active input. Once I switch to the other input it only listens to commands from that other input. I really wish - and had hoped actually - that the monitors would listen to DDC commands on all inputs, but at least on my monitors they don't. And it sort of makes sense that only the active input would have it's I2C bus routed to the uC to listen...

[JustinCEO]

Only being able to send commands on the active input does make some intuitive sense. I guess I just assumed you'd be able to switch the inputs back and forth from the same Mac.

[kfix]

This is my experience as well.
I guess it warrants a note in Caveats, but that section would be at risk of growing a mile long...

[jpeeler]

Just to add a data point, I have an external Samsung U28E570 connected via Mac/HDMI and PC/DP. I'm able to switch back and forth using the Mac.

[sufinawaz]

Facing the same issue on a DELL2412M monitor between mac and windows where i cannot switch from windows (svideo) to Mac (displayport -> usb-c) but can from mac to windows

[jnpatrick99]

On LG 27GN950-B this utility does not work at all for switching monitors. Monitor blinks and then gets to the same input again. I tried all output values - nothing works.