Ngalert error - invalid format of evaluation results for the alert definition

I’m getting an error from an ngalert:
invalid format of evaluation results for the alert definition : frame cannot uniquely be identified by its labels: has duplicate results with labels {}
Any suggestions/hints as to what that means?

Never mind, figured it out. we had the alert triggering off of query A (which returned a lot of data) instead of B (which was essentially “last of A > 0”)