This is a bit of a strange one. I've heard of the "last seen" not updating but not the follow date not updating. You could try refreshing all your followers from the "user database" tab to see if that helps.
To do this, go to the "user database" tab, right click in the white space and click "Refresh all followers". This should hopefully pull a list from the Twitch API which may or may not correct this issue.
