if anyone is still interested in this topic here is some relevant information :

• We should not declare a custom field of class FilterSet in attribute Meta.fields.
• If we create a custom FilterSet class we should declare it in the view using the filterset_class attribute - the author of the post does not do that.
• The lookup declaration of the DateFromToRangeFilter field is provided automatically using the <field_name>_before and <field_name>_after lookup - so there is no reason to override this.

Let me also add a comment on how to declare filters in the view:

• on one hand you declare filtering search_fields, and on the other hand you do exactly the same in your FilterSet - why ? the sarch_field attribute provides us with lookup logic icontains by default - link
• as I partially mentioned you are declaring an attribute filterset_fields but you have created a custom object of type FilterSet - we should use either one or the other.