My D7200 is set to "Back Button Focus", by pressing the "AE-L/AF-L Button" to activate it's focus, and it will not activate when it is pressed, "all of a sudden"; since I made a change, in the camera's settings.

The camera's focus, is set to: AF Continuous, and Focus is on Single center point & A4 Autofocus Activation IS set to Auto Focus ONLY.

Pressing the AE-L/AF-L Button doesn't activate focus operation in any camera mode.

Only when I set the camera to modes: U1 and U2, will the Back Button focus function operate.

If I go into it's menu, and set it to focus, using it's shutter button, it'll focus properly, with the shutter button!

It is set correctly, to use in Back Button Focus mode. Yet, it simply does not, operate, at all.

What I did to the camera, right before this problem began, was I went into it's menu; and I was in it's...

CUSTOM SETTINGS MENU: and in there, I had gone into the f: Controls Menu....

In there, the first item listed is: "OK button"...

In the "OK Button" setting, there are three items; The 1st one is, "Shooting Mode"....

I'd selected that one, and it gave me 3 options:

1) RESET Select center focus point
2) Highlight active focus point
3) None

My camera had been, set to the setting, for "Highlight active focus point", and I changed it, to:
"RESET Select center focus point"

I DO NOT KNOW WHAT THAT "RESET" MEANS...DOES "IT" RESET? DO "YOU HAVE TO DO A RESET"???

There are two other changes, that I made to the camera, but I don't think they could've of had anything to do with this issue. I set the Preview and the Function buttons to be Spot Meter and Exposure Hold & Lock, respectively.

After I'd made these THREE changes to the camera, I tried using it, and the Back Button Function, no longer operated. Yet, it's setting was still intact. When I tried setting the camera to focus, using the shutter button,
it did operate OK, in that, way.

When I set the camera's Mode dial, to previously stored, "U1 & U2 Settings," the Back Button Focus did, operate properly, yet, when I again, took the mode dial back off, of those U1 & U2 settings, and put it back, onto any other setting, the camera would again, not Back Button Focus any more.

I'm trying to avoid having to do another reset on this camera if possible, I've had to do several in the past, for other things similar to this.

Any ideas or suggestions?

Thanks.