[uiri]

That bug mentions that Facebook is also broken.

I am kind of surprised that the sites you mention can implement the spec correctly but Facebook and Google can't.

[phyzome]

Google is notorious for not following spec.

In this case, though, what happened is that Google implemented a different, earlier version of the spec than most everyone else. Mozilla is busy implementing that spec as well to bridge the gap.

[Dylan16807]

Google's CardDAV server isn't standards compliant (2014) https://news.ycombinator.com/item?id=16412730

I'm not surprised.