Index: src/bp-groups/bp-groups-activity.php
===================================================================
--- src/bp-groups/bp-groups-activity.php
+++ src/bp-groups/bp-groups-activity.php
@@ -400,6 +400,7 @@
 
 	groups_update_groupmeta( $group_id, 'last_activity', bp_core_current_time() );
 }
+add_action( 'groups_join_group',           'groups_update_last_activity' );
 add_action( 'groups_leave_group',          'groups_update_last_activity' );
 add_action( 'groups_created_group',        'groups_update_last_activity' );
 add_action( 'groups_new_forum_topic',      'groups_update_last_activity' );
Index: src/bp-groups/bp-groups-functions.php
===================================================================
--- src/bp-groups/bp-groups-functions.php
+++ src/bp-groups/bp-groups-functions.php
@@ -165,8 +165,6 @@
 		$member->date_modified = bp_core_current_time();
 		$member->save();
 
-		groups_update_groupmeta( $group->id, 'last_activity', bp_core_current_time() );
-
 		/**
 		 * Fires after the creation of a new group and a group creator needs to be made.
 		 *
@@ -193,7 +191,7 @@
 	}
 
 	/**
-	 * Fires after the creation of a group.
+	 * Fires after the creation or update of a group.
 	 *
 	 * @since BuddyPress (1.0.0)
 	 *
@@ -502,9 +500,6 @@
 		'user_id' => $user_id,
 	) );
 
-	// Modify group meta
-	groups_update_groupmeta( $group_id, 'last_activity', bp_core_current_time() );
-
 	/**
 	 * Fires after a user joins a group.
 	 *