I don't believe anyone mentioned this yet so... here goes nothing, there is a suspicion that this is due to A/B testing

This is a bug report from the Invidious project; this is back in June 6 (so four months ago), but the hoster of a fairly large instance noted a very bizarre error message on the Invidious project...

Conclusion is that Youtube is very likely rolling out A/B testing of requiring all clients to login before viewing videos

Refreshing will probably work considering this is most likely result of an A/B test, but unfortunately I don't see a way of this problem going away

Sometimes I get that prompt while on vpn. After refreshing the page, I'm able to see the video.

I get why I got downvoted for having posted a YouTube link on [email protected]

Oh that's how they broke invidious

It's a VPN thing. I have a work VPN that gives me the same error on piped API front ends like piped.video

If I use my regular device without a VPN the alt front ends work fine.

Bots can't watch videos anymore? Anti-droid discrimination

SmartTube, my go-to way to watch, is having issues again today too. I presume it is to make people subscribe to YouTube premium but my first thought was to use Nebula instead.

This can be a soft limit where Youtube limits the connection rate so that artificially inflating view count becomes more costly. There are inexpensive 'services' especially in India or Pakistan where you can buy human (like a whole internet cafe) view times to your scam video to make it float in suggestions and to promote a channel.

I don't work for youtube so it is just a guess.

This has always gone away for me when I change my location in my vpn.

Been seeing that a fair bit too lately. Freetube, Grayjay, and Newpipe seem so sometimes get around it, even if the error is in the browser the video will sometimes load in those apps from the same IP. If you get lucky and find a working invidious/piped instance that might work too.

Otherwise, turning on a VPN and switching between servers will usually eventually lead to a working one. That, and if you're up for it, check to see if your favorite creators are on places like Peertube, Odysee, or Rumble that don't block IPs like YouTube does.