Grafana alerts not being triggered always

I have installed Grafana on a RPi4 using the docker image and configured to to receive data from influxDB. Everything works as expected. I later configured Slack for alerts. I notice that “some” of the alerts are being missed. Perhaps I don’t fully understand how the alerts work. The attached image shows a scenario.

I was expecting an alert to be fired between 23:00 and 00:00 however it didn’t. Also, I don’t understand what the green line signifies at 22:00. I earlier had “Evaluate every” 15m. When that failed, I made it every 1m expecting it to be more reactive.