Comment (by Roland Haas):

Though looking at the code that is used for the MultiPatch_GetBoundarySpecification case, this seems incorrect as well. If called in LEVEL mode it will set all boundary widths to 0. And when called in SINGLEMAP mode (so that map is defined) you would end up selecting boundary conditions more than once which makes Boundary abort.

Something similar to what is done when going from GetBoundaryWidths to GetBoundaryWidth seems required, ie.:

  if (CCTK_IsFunctionAliased ("MultiPatch_GetBoundarySpecification")) {
    int const maps = MultiPatch_GetMaps (cctkGH);
    for (int i = 0; i < 6; i++)
      nboundaryzones[i] = -1;
    // collect all boundary information from all maps, and get 
    // outer boundary information only
    for (int m = 0; m < maps--

Ticket URL: https://bitbucket.org/einsteintoolkit/tickets/issues/2288/leans-boundary-condition-setting-for-bssn