Lightroom can't control Nikon lens aperture during tethering

Hi!

When connecting my D850 to Lightroom (Classic 12.5) on a Mac, I find that the aperture closes and opens randomly when using my 105mm Macro Nikon 2.8. It doesn't matter whether I try and change the aperture in Lightroom or on the camera.

This lens and body works fine when not tethered - and using a different lens is also fine. I installed the latest firmware for the camera body but that doesn't seem to have helped.

Please help!

Dan