No "add user" function after android update

[AC Question]

I got my daughter a Lenovo s8-50 tablet for her birthday a couple of months ago. Created a user account for her with me as the admin so I could set up parental controls, disable purchasing etc. All was good. Until a few days ago when the tablet updated the android operating system. Now there is no function to add another user. It's just not there, even though looking at info there should be a "users" option in the settings menu. Any advice? Now my daughter cant use her tablet as theres all sorts of things popping up and I don't want her using it without restrictions in place. Thanks in advance for any help. Rachael.