Do you have any photos?  (is it actually on his nose or more like on his forehead?)  If there are any red spots, it might be that the other bunnies are nipping the hair out (and with only nose hair, you wouldn’t see tuffs). I had a bunny rip another bunny’s lip and eye lid, so be sure to keep safe distance between the cages. 

   Also, it’s not unusual for some rough grooming.    Jack used to chew/pull fur when he groomed.  His partner bunny taught him not to do that by pulling away and not giving attention.  So they could be also trying to groom through the bars and that is the only place they can do it that way — so it makes sense that fur would be missing there via nipping or grooming. 

This is the time of year that bunnies do molt and it’s not impossible to start at the actual nose and not see it anywhere else, but it’s unlikely. 

So I am thinking this is something going on between the bunnies via cage bars.  You could find out for sure by putting some sort of wire netting around the base so they can sniff each other but can’t over groom or nip.  Bunny hair doesn’t grow back right away – it grows in spurts, so you may have to wait a while to see if that is the issue.  (Maybe by then they would be bonded). 

When Zane is in his cage and the other two come up  to his cage does he get territorial or anything?  Does he put his nose through the bars? Or put his head down to be groomed?   Just trying to get a feel for his behavior while he is caged and the others are out.  

It could be something going on between the cage bars, or it could also be a fungal infection like ringworm. Is the skin flaky at all or does the skin seem healthy otherwise? Any signs of bald patches in other areas?

In the first picture, it looks like you can still see some very short fur in the bald area, like fur follicles (i think thats the right word). It really does look like it has been ripped out or chewed off, to me. Since the fur there is short, you wouldnt always see tufts of fur on the ground