If we enabled userStore sync before CSAT or at the same time this is fine, but if not we probably want to enable this only after that. There is also an issue about handling older clients trying to update user store in general. I've left a comment about this general issue here.

For this specific case it would probably be better to make sessionChange.currentUserInfo an optional field and change the keyserver so that it will only send it to older clients (and finally remove this code completely from the client codebase).