Monitor connection issues - DP to HDMI cable

I am having problems connecting a monitor HDMI to a PC DP. (The monitor at issue is bolded below.) This is my setup:

OptiPlex 9020 - 2 graphics cards

- integrated with DP and VGA ports

- discrete with DVI and DP ports

3 monitors

- S2316H with VGA and HDMI ports

- ST2220L with DP, HDMI, DVI, and VGA ports

- U2419HX with DP and HDMI ports.

This is the configuration that I currently have:

- PC>>>VGA from integrated>>>S2316H VGA

- PC>>>DVI from discrete>>>ST2220L DVI

- PC>>>DP from discrete>>>U2419HX HDMI

This configuration works, but I want to get rid of the VGA connection and use DP-to-HDMI instead.

Here's my problem: The DP to HDMI adapter cable works when connecting the U2419HX or the ST2220 to the PC, but when I use the exact same cable to connect the S2316H to the PC, the monitor is not recognized. I've tried both input source settings - auto and manual (HDMI) - and neither works. I don't think that the cable is bad because it works with the other 2 monitors. What am I missing? Could the HDMI port on the monitor itself be bad? I couldn't get this to work when I first bought the monitor either (of course, warranty has long since expired).

Thank you. Any help would be greatly appreciated!