D850 electronic VR - what stops it working?

Hi all. While I remember, and with trepidation because I don't have my camera with me...

On a recent trip I unusually tried to shoot video (of Skookumchuck rapids), and since I was shooting hand-held it occurred to me to try to use the D850's "electronic VR".

However, nothing I tried allowed me to enable it. I was in 1920x1080 normal frame rate mode (I think I tried 1280x720 too). I tried VR on and off on the lens. I tried at least two lenses. I tried different sensor crop sizes. All I got was "electronic VR is not available with your settings" (or words to that effect), but no explanation. I was in manual exposure with auto-ISO, but I think I tried manual ISO too.

Has anyone tried it and worked out what things upset it? I know it won't play with 4K or high frame rate, but I can't spot a more definitive list of limitations in the manuals (which I had on my phone while trying to enable it).

I imagine I may have a "d'oh" moment coming. Thanks!

Ah. Not knowingly, but possibly. I may at least have enabled it for stills photography at some point, and left it on since it doesn't seem to do anything unless you put the camera in manual focus mode - I don't know why, because it would be useful in AF to know where the camera decided to focus. If being on but not doing anything still disables electronic VR, that might well explain it - for some reason my manual searching had failed to come across that interaction.

I'll check when I get home, and report back with either the expected "d'oh" or further confusion. Fortunately I had a tree to lean against when I was videoing rapids, but it would be nice to know for future circumstances.

Okay, thanks - confirmed that it was the focus peaking. Which a) is on a separate screen from everything else so I didn't see it, and b) wasn't doing anything anyway because the camera was in autofocus mode. Anyway, peaking off, VR on.

That's a bit irritating, but I guess it's more "feature" than "bug" since the interaction if AF was switched on or off would also be confusing. Oh well, now I now. I wonder why I didn't find that while trying to search the manual? (It would be nice if the on-camera help had said a bit more...)