Given an appropriate image -- The Auto adjustments (auto-tone, auto-contrast) work for me in Grayscale, you do not need to convert to RGB to use them. Given an image that doesn't need much adjusting, the adjustments don't do much noticeable change.
Do you have a grayscale image that is auto-corrected better after converting to RGB?
I'd like to test it out for myself if you do!
For my image testing, after converting to RGB from grayscale, the changes made to the image with the adjustment layers on was basically the same visible changes made to the image after turning off the layers, then switching to RGB, and turning the adj layers back on.
Maybe you could record a video if the odd behavior you're seeing?
I'm working from a original b&w, not a conversion to b&w although it doesn't make a difference.
Yes auto tone, contrast does work in grayscale but auto Curves, Brightness/Contrast and auto Levels all require me to change to RGB to be used. Manual changes work fine in grayscale. This is true both in Adjustment Layers and Image>Adjustment.
I am not acquainted with the video method. I assume you are not referring to actually setting up a camera and watching me tweak, right?
And yes, I do have one, actually many that exhibit this behavior. But as I said, try it using Adjustment Layers or Image>Adjustment first. It should show up.