It looks like a failed key replacement during a scheduled maintenance event. Normally this sort of thing is thoroughly tested and has multiple eyes on for detailed review and planning before changes get committed, but obviously something got missed.
Would be interesting to know how something could get missed. You'd think the system was set up so that new keys could not be published without being verified working in a staging system.
Would be interesting to know how something could get missed. You'd think the system was set up so that new keys could not be published without being verified working in a staging system.