An issue was reported in davidalber/geneagrapher#36 in which a record with a promotor and co-promotors was returned with no advisors. I hadn't seen a record with a co-promotor or promotor before, so it's not surprising these weren't recognized. The example record provided was https://www.mathgenealogy.org/id.php?id=51506.
Reproduction:
Retrieve and extract the 51506 record.
Expected: an advisor list of [51477, 51475, 32787].