There is apparently a recognised bug with group rides at the moment where not all avatars appear in the group kit for the ride. I suggest this is not necessarily a bad thing.
I can see why you might want to have everyone in a group ride wearing the same kit when they are riding with everyone else who happens to be on Zwift at the same time. It makes it easier to see who is on the group ride with you and who is not.
However, when a group ride is on ‘closed roads’ (or whatever its called) this is not necessary as everyone you can see is on the group ride. In this situation it is actually a disadvantage. Having everyone in the same kit makes it harder to pick out your own avatar and the avatar of other riders which you might want to be able to easily identify (a friend or perhaps someone you are determined to beat in the next sprint - whatever).
It seems to me, the only reason to put everyone in the same kit where the roads are closed is for promotional purposes on sponsored rides. Rides which are 'brought to you by [insert sponsor name]. (In what sense a group ride, is brought to me by a particular sponsor is beyond me - I pay a subscription to ride Zwift. Pretty much anyone can arrange a group ride. It just seems like a way for whoever organised the group ride to put a few dollars in their pockets).
Personally, I have no interest in wearing an advertiser’s kit for the duration of a group ride. At least, where group rides are on closed roads I would much prefer to be able to wear my kit of choice. Pandering to advertisers seems to be the only reason to do otherwise.
Even on group rides on open roads it would be my preference to wear my kit of choice.