Stuff like the black flickering on Freesync, I experience with the same screen in that video on my V64. Games/Driver depending.
Apparently it can be fixed using CRU to modify the freesync ranges, I've not yet tested this though. But I can understand why that would fail Gsync validation, and I don't think it should be acceptable point blank.
Obviously Jen's wrong in his assessment that Freesync doesn't work. But it's certainly not as rosy as some would have you believe.
Like I said above Freesync is from having its faults and the same for Gsync it's also far from being perfect and users report same issues.
Had a little Google and you can find anything about Gsync that has also been reported by Freesync users.
Black screen flickering, is it common? Probably not is your issue common again probably not.
It just proves they are not free from gliching out.
Edit
Couple weeks old, Nvidia driver breaking Gsync
You know what I wanted to add videos of Freesync but it would seem they isn't much to go off from YouTube. I wanted to keep the search fair so I got videos up from 1 month ago and am surprised just how much Gsync videos they is showing up.