Issue With Buttons on Z6III's Battery Grip

[ckqualls]

So, I went into menu f2, Custom Controls (shooting) to program buttons on the battery grip. When I try and program the AF-ON button for back focus on the battery grip (selecting "Same as AF-ON Button), it doesn't focus. Camera is set up for back focus. Tried with both Nikon 200-500 and Nikon 24-120 f mount lenses. Am I missing something, or is there a malfunction? Thanks.