Bestway pool pump

When I put it on recirculate, it has really really strong flow but as soon as I put it in filter mode, it barely flows at all, and I’ve opened it up and cleaned the polyester balls out and I don’t know what to look for. So we know that the impeller works because of the flowwhen it’s recirculate, so we know that it has apparently clear and let an outlet but as soon as I put it in filter mode, it barely trickles out. I turned the pump off, go back to recirculate and it’s phenomenal so where can I look to see if there’s an obstruction somewhere thanks in advance.