CheckboxSelectMultiple not displaying checkboxes with Django-Material

I'm fairly new to Django so please bear with me.

I'm using a ModelForm along with Django-Material (By Viewflow) and it's working really well expect for one thing. It doesn't display checkboxes.

My 'Person' model has a ManyToMany relationship with 'Problem' and I've set the form to show checkboxes as so -

class PersonForm(forms.ModelForm):
class Meta:
    model = Person
    exclude = ('',)
    widgets = {
        'problems': forms.CheckboxSelectMultiple(),
    }

But it shows up like this

When I remove the Material template the checkboxes show up properly

I'm not really sure if there's a problem with Django-Material or something I may have missed. Help would be really appreciated, thanks!