Drupal Commons, can't break-contact error
to resolve this problem, two patches are needed:

1  patch for the trusted contacts module as discussed in comment #2 here: 
https://www.drupal.org/project/commons/issues/2588155

2... and a patch for the membership-delete-action
 .../profiles/commons/modules/contrib/og/includes/actions/membership_delete.action.inc
as discussed here
https://www.drupal.org/project/opigno_lms/issues/2953675

works for me...
d