The list of users was been lost during migration, you need to add them back.
I guess it's the same with old discussions (but you can navigate on your previous posts easier for the ones created after migration).
You can edit your profile at menu 'your stuff' -> Profile and then on the menu on the right click on edit profile and privacy.
It is not fair isn't it? Strange that list of friends has been deleted. I don't remember few who were there in my friends list. How I am going to find them again? I think if there is no other way then I need to recollect one by one and then add it. If there is no other way of getting that list back.