I have a D3400 and recently I haven't been able to change the aperture on any of my lenses in manual mode. I have lenses with aperture rings and if I set the aperture to anything below the largest aperture such as f/16 and put it on the camera, the aperture opens back up to f/1.4 by itself.
This problem just started. Every lens that I use is unable to change aperture. If I mount the lens, the aperture is forced wide open, even if it's set to f/16 on the lens. When I press the shutter it stays wide open. Whether I use the viewfinder or live view, the behavior is the same. And once I remove the lens, the lens closes back to f/16.