It seems like users can be randomly selected more than once, however the 'Previously picked' list does not show repeated users. When a user is randomly picked again the name shown in the 'Previously picked' list is wrong.
It seems like whenever a user has been picked they're removed from the list used to display 'Previously Picked' which is wrong.
To test just join a meeting with 4-5 different users and pick a few users with this plugin. The bug should be obvious.