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

My servers are working fine. When I’m bypassing Cloudflare by deactivating the orange clouds everything works better and faster with no 502-bad gateway errors.

Updates:

  1. Cloudflare system status
    [Scheduled] Our dashboard will be undergoing essential maintenance on December 4th, 2017 from 22:00 - 23:00 UTC
    Cloudflare Status - [Scheduled] Our dashboard will be undergoing essential maintenance on December 4th, 2017 from 22:00 - 23:00 UTC

  2. Incident History
    Cloudflare Status - Incident History

I don’t know what Cloudflare has done but all troubles on our sites happened right after the updates. And also noticed that old data (!) was loaded. All new changes that we made to our css, etc. were replaced by old ones (from week before update!).