Happened to me just today, And whole day long GW2 game client used to work. It stopped just an hour or so ago.
(No, I haven’t been updating my Mac OS and i do not intend to for a good reason. The game i pay for was working with my OS for about half year and stopped to work without any notice beforehand. I believe its not intended by game devs.)
P.S. Submitted a ticket to support. Fingers crossed.