BuddyPress.org

Try installing Email Log (https://downloads.wordpress.org/plugin/email-log.zip), which records all mails sent from the WP+BP installation, this will at least let you know if the activation email has been processed from the Site (According to the site itself).

There is also another plugin (https://buddypress.org/community/groups/wp-activate-users/) which will allow you to activate users that dont seem to get the email or are just plain lazy.