There is nothing in the monitor to cause this. A video card driver change could cause this. To what port on the computer is the left monitor connected? And the right monitor?

As I look directly at the back of the PC, my left-hand monitor (the problem child) is plugged into the port on my right.  The right-hand monitor is of course plugged into the port on my left.

Thanks!

Swap them on the back of the computer and re-test. Does the issue follow the problem monitor when connected to the other port? What is the Optiplex service tag number?

I did as you suggested and the issue remained with the monitor on the left (that's my left as I sit at my desk looking at them).

So you are saying that both monitors have the same issue when tested on that one port on the rear of the Optiplex? Yet when both monitors are tested on the other port, they are fine? If yes to both, then the monitors are not at fault.

Yes to both.

Ok, so now that I know the monitors aren't at fault, how do I fix the issue?

Granted it's not the end of the world if this continues, it's just an annoyance, but there must be a way to make that message stop???

since it started about a month ago, you need to investigate which driver update was installed then that caused the issue. Then remove it and use its older driver.