I think it's one of two things:
1) Something has failed in the valve, like one of the walls, or, as always, the spider gasket.
2) It's assembled incorrectly.

In waste or backwash mode, the flow out to your waste outlet should be as strong and powerful as your normal filter or recirculate pressure to your return. When it's in filter or recirculate there should be no water through the sight glass.