This is simple, and each cause will have a different level of impact.
For instance, if your ads have stopped showing completely (check impressions), you know you have eligibility issues. You will also most likely see a warning message about the eligibility issue.
You will see you have impressions, but the flow of calls and messages has reduced.
Further, if you see that overall market impressions have reduced, it would mean a drop in demand.
Finally, lead quality is obvious: you have the same lead flow, but conversions have dropped. You will need to track your ROI (or ROAS) for this one.
