I've been having some issues with the kavin.rocks lately too, it seems pretty intermittent. If it's not something on my end that I'm unaware about, I think it may just be extreme load. There's been a lot of exodus lately so I wouldn't be surprised if there's just more traffic than usual across all of them.
Invidious is broken up into multiple instances, each instance can go up or down at any time and could be blocked by Google/Youtube relatively easy – usually just a matter of hopping to a new instance that hasn’t been blocked yet
less likely (but not out of the realm of possibility) is DNS shenanigans – ex. archive.today and Cloudflare have a pretty adversarial relationship, trying to get to one of the archive.today instances using Cloudflare DNS (1.1.1.1) can be a crap shoot