When viewing the Comments tab in Switcher Studio, you will see user names next to their comments, if you are streaming to a Facebook Timeline or Page. However, if you are streaming to a Facebook Group, you will only see "Facebook User" on each comment, as shown below.
Unfortunately, this is a Facebook restriction and not something that Switcher Studio can change. The restriction was part of Facebook's privacy overhaul in May 2018.
Although you cannot see the person's name as they leave comments in a Group, you can still respond to their comments while live by reading the comment aloud and answering it without addressing the person by name.