Today (in stackoverflow), Each question has answers in unsorted way, before that I see the answers of each question in sorted order (by their upvotes), is this a settings? if so how do it? and if not are you seeing same as me?
Just above the list of answers for any post, you will see the tabs 'active', 'oldest' and 'votes', which represent your desired ordering of answers. Click on the one that says 'votes'.
I would imagine that you had previously (mistakenly) clicked on 'active' or 'oldest' to change your default ordering. This setting does appear to be persisted across different posts.