Admin unable to change user’s role

Hello 

I am the administrator of a website in which we assign roles to users and then define which products each one can see. 

I am trying to change the role of the users but it does not work.

My process is as follows, I enter the user’s profile I remove the check the role they have currently assigned, I check the new role they should have, I hit the update button, the page refreshes and the change does not take place, the role they had and I had removed is assigned again.

I am not able to change the role of any user.