502 Bad gateway errors of 10 Wordpress websites at same time after Cloudlfare update this week

This is mostly a customer forum, so I suggest you open a support ticket at support.cloudlfare.com orlogin to Cloudflare and then contact Cloudflare Support.

A 502 is typically an issue on the origin server, but you said you haven’t made any changes. Though if it’s shared hosting, the host may have changed something. Here’s a support article on that error:
https://support.cloudflare.com/hc/en-us/articles/218378978-What-should-I-do-after-seeing-a-502-or-504-gateway-error-on-my-site-