Basically, all ru. TLD became failing for all dns resolvers that use DNSSEC (which is the most of them)

As user, I am unable to visit any pages on .ru domains, as their IP would not resolve.

Reason is highly likely mistake (human side) in signing procedure, not something time- or hack- related.

Someone is most likely CC for TLD RU, aka АНО КЦНДСИ, official registry of .ru TLD.