What steps did you take to find the problem?
This is obviously a modeling error. Set a breakpoint. Investigate the values of $PeopleWeSupport. It should be fairly obvious why such a retrieve goes wrong.
In my experience, you sometimes need to trigger an error twice before it shows up in the application log. You can replicate this by adding a button which triggers this microflow and just press it a few times. See what appears in the log.