With the last version of this theme this warning is shown when I go to Activity or Members pages and I'm not logged in:
'Warning: Cannot modify header information – headers already sent by (output started at […]/wp-content/themes/bp-social/activity/index.php:12) in […]/wp-includes/pluggable.php on line 934'.
When I'm logged in it goes well. Also with the previous version.
In BuddyPress Social Theme Options, BuddyPress Settings, Global privacy is enable (only logged in user can view members profile and members directory) as it's shown in the screenshot. When it is disable, everything is ok.