This attitude will help ensure your students have less problems online.
The sentence above is taken from an online test provided by the University of New South Wales.
I am sure that less is not the comparative degree of little meaning minor here. So less must be a determiner here.
In my opinion, fewer problems is correct and less problems is not because less is used with uncountable nouns. I know that in everyday speech less problems can possibly be. But how appropriate is this casualism (if I can put it like this) in a test?