I've had some issues with Windows 10 and ffxiv but nothing that makes it unplayable.

First I had the issue with not saving my username, but I set ffxiv as a trusted site which fixed it.

I've had an issue where my game will occasionally freeze for like 0.00001 seconds, not that big of a deal and a barely notice it but it did get me killed in Titan ex once.

The last issue is the game bar, first time I used the game bar it worked, but any time using it after that it just gives me an error message that says it was unable to change my settings and to try again later.