Cannot create Classification Attributes from IP Classification Editor

Hello, 

I do not understand why some users can create Classification Attributes from IP Classification Editor (having the + button) and other users cannot perform the same operation as the + button does not appear (see images). 

The users have all the same credential and they all work on the same collaborative space. 

Have you any suggestion? 

@VA ​​​​​​​@MV ​​​​​​​@AF ​​​​​​​

Classification ​​​​​​​Classification Manager ​​​​​​​Classification Attribute ​​​​​​​