Not a bug. It’s a change that has been announced more than a week ago:
https://forums.funcom.com/t/changes-to-steam-family-sharing-settings-on-pc-official-servers-with-update-2-1/144074
You cannot continue using official servers through a family-share account. You can only connect to them on the main account, the one that has bought the game.
You can still play single-player, co-op and on those private servers that allow it.