One user out of a sudoers group cannot run 'su -'

Issue

• The user 'user2' is not able to run the following command:

$ sudo su - user3

• This user belongs to the group admingroup which has following configuration in sudoers file
  %admingroup ALL=(root) /bin/su - user1, /bin/su - user3

• Other users from the group are able to run the command, but not this user.