BuddyPress.org

On what hook are you firing that function? Are you using the Legacy or Nouveau template pack? (Have you changed from the Legacy to Nouveau template pack recently?)

It could be a number of things, but my first thought is that there’s no reason to be changing the groups nav when you’re in the middle of the create routine, so maybe there’s a more strict check we should be using above and beyond the bp_is_group() check as used on the API page: https://codex.buddypress.org/developer/navigation-api/#change-item-names-of-users-and-groups-nav-menus

In any case, you should be able to prevent the error by adding a conditional around calling edit_nav():

$bp = buddypress();
if ( isset( $bp->groups->nav ) ) {
	$bp->groups->nav->edit_nav( array( 'name' => __( 'Home/Reflections', 'buddypress' ) ), 'home', bp_current_item() );
}