I have a blog at http://www.kingstonnexus.ca that I have Buddypress installed on. I've been having trouble making Buddypress more compatible, but that's not the issue I have.
Buddypress, once set up, allows anyone to become a user. I currently have 28 users, although when I go to http://www.kingstonnexus.ca/members/ it displays 25 out of those 28.
Since they have signed up technically as WordPress users of my blog, I believe this is a wordpress issue not a buddypress one.
One of the members brought this issue to my attention, he is one of the 3 that don't show up on the members page. He also cannot log in even though he has the correct username and password, the same permissions as everyone else, and shows up in my dashboard as one of the users.