I have my Pi setup in your control panel to notify me after 6 hours of non-reports. I discover I wasn’t feeding and in fact my Pi wasn’t even reachable on my local network. A power cycle fixed that.
But I am wondering whey I didn’t receive a notice? Based on your graphs it looks like it was down >24 hours. In the past I have gotten an email notice when I was offline (I started with a Pi 2 which had frequent issues, the Pi 3 has been much more reliable and I wasn’t checking it manually that often).