Thanks you for the additional information.
I see at the screenshot the bbPress roles in the list of the blocked roles. Users may have more then a single role granted at the same time. Take into account that when some roles are blocked for the role A, user with role A sees at the “Users” list only users who have allowed (not blocked) role(s). Thus, if new created user has the secondary bbPress role ‘participant’ assigned, user with role A will not see such user, as one of his roles is blocked for him.