They will never fix the friends list. They won't even acknowledge that it's an issue. You'll have to have all your ESO friends in the same guild to bypass this.
They broke it since imperial dlc and it still broken when they release orsinium dlc, now it will remain broken when they release the thieves guild dlc, do we have to wait to see of ZOS might fix it when they release dark brotherhood dlc?
They changed how the list works at Imperial DLC to fix previous issues. Friends list works for me .....
Friends have to be on both lists to show up on the in-game friends list. The list will not show people you have as a friends but they do not have you as a friend.
Also in order to for the friend to show up, they need to be online the same time as you. After that they will show online/offline in the list.
If you delete your saved data, it will clear the list. It will be empty until they login while you online.