I think the offline capabilities of Mendix are not yet ready to filter on the Date attribute (and probably it was possible before). So if you don't want to use offline capabilities in your app, just use XPath as datasource for your datagrid. And if you do want to use offline capabilities in your app, I think your screwed. You should definitely send in this as an idea on this forum to get this on the agenda as feature request.
For those interested I added an Idea requesting this possibility: https://forum.mendix.com/link/ideas/918