Losing connections is an expected reality of persistent connections over the internet. That is why cloudflared establishes 4 connections to 2 different Cloudflare colos, so that the likelihood of all 4 going down being very, very small. As long as 1 is still up, Cloudflare will still route incoming requests to your origins.
What happened yesterday during that incident was that connections could not be (re-)established due to an embedded certificate in cloudflared that had expired. That was the unfortunate problem that was lying in there for several years.
We could roll a fix across the edge but only for sufficiently recent versions (2019.11.3 onwards).
During that period, cloudflareds would still receive traffic normally, they just would not be able to re-establish their connections if lost. Most cloudflareds had at least 1 connection still up and did not notice the incident therefore.
I hope this helps understand what happened. Having said that, we’ve obviously learnt a hard lesson and will roll out new checks across our automations to check for embedded certificates so that we can upgrade them well in time so that releases have them always with expiration far in the future.