Alerting on percentage_diff() not working

So the end result is to get an alert when we have 2 times the traffic within a 48 hour period. I’ve been playing around with the alerts and am thinking I do not understand the percentage_diff() condition. I started by testing at just percent_diff() above 10 and was getting alerts, then increased to 20, and no longer get alerts, when the graph clearly shows that the data is above the threshold (pics included).

Am I not using percent_diff() properly? Datasource is Prometheus, if that makes a difference.

Any help/insight is greatly appreciated