Typically this results from either an inport of invalid data, or a bad merge of father and son with the same name. Detection of invalid/circular relationships (as well as impossible dates on people in birth/marriage/death relationships) is something I've been asking for, a very long time, I'm told it's on the list of improvements. Wondering how difficult it would be to add a new Bot which searched for those, similar to the current MatchBot. It would go a very long way towards improving the quality of the data on WikiTree.
Thanks Michelle for fixing.