They only recently rewrote their core in Rust (https://blog.cloudflare.com/20-percent-internet-upgrade/) -- given the newness of the system and things like "Over 100 engineers have worked on FL2, and we have over 130 modules" I won't be surprised for further similar incidents.

The irony of a rust rewrite taking down the internet is not lost on me.

20% seems to grow every time someone write about this.