I just took a quick look at some internal analytics on errors. Looks like we are seeing a large number of 522 errors, a small number of 520s and for a brief moment (perhaps when you did the upgrade) a huge spike in 521 errors.
https://support.cloudflare.com/hc/en-us/articles/200171906-Error-522-Connection-timed-out
A really brief and not statistically meaningful spot check showed a large number of the 522 errors over the past few hours coming from bots (Yandex, teh Googles, etc) which if you look at the 522 possible causes could indicate the crawlers were exacerbating an existing load problem… so I might work with the host on load first before network in terms of troubleshooting.