I was surprised this wasn't part of the lessons learned. But it seems the monitoring basically failed but that wasn't a lesson.
I feel like majority of uptime monitors are falling for this same trap. One of the reasons why for my monitoring service I choose to do full page load monitoring via Chrome instead of just a http request via Curl or whatever. Main reason, people care if the webpage loads or not. People care how long it takes for their webpage to load. Having a website respond in 200ms is great but if it takes 8000ms for all the JS to load and process your website is still slow. I get why sites are just doing curl requests because it's way cheaper but really you're monitoring one part of the stack while really caring about all of it. If your website starts producing javascript errors you want to know, etc.
[1] https://www.ootliers.com (The landing page and everything are terrible and I'm working on improving that)