I've been using my Nikon D5300 for about 1.5 years and have recently started to use it for some video work as well. I realized that when manual movie settings are turned on and you go to live view, you
Cannot change the shutter speed to every value - it must be faster than the number of frames per seconds; e.g. I cannot go below 1/30th when shooting in 24 fps. This makes sense to me and isn't a problem anyway because I use the 180º shutter rule (i.e. shutter speed = 1/(2*fps) which is 1/50th for me).
Cannot change aperture at all. This is more of a problem, but can be solved by switching live view off, changing the aperture and the go back to live view. I wonder why manual movie settings prevent you from changing aperture in live view?
Update Here is some additional information:
This "problem" occurs both with my 18–55mm Kit Lens (AF-P DX 3.5–5.6G VR) and my 35mm lens (AF-S 1.8G)
Apparently, you cannot change aperture at all in live view (at least in my camera). However, I can change the aperture value when manual movie settings are turned off — the number displayed changed and the photo will be taken at the aperture I set. This is not possible with manual movie settings — the aperture number just "freezes" and cannot be changed.