The subscriber counts here are a bit dodgy. I think it is only showing the subscribers on the instance you are in, not overall. I accidentally went to my other group from this account and thought it had dropped from about 200 subscribers to 3! It makes me wonder how many subsribers we actually have here, if the 358 showing is just people subscribed from this instance we may actually have quite a few more. Although I think the users/posts/comments counts are really more meaningful anyway.