I've seen a video of this problem before:
Stenner Pump not pumping bleach - YouTube
The cause was never confirmed, but the guy did solve the problem by taking the setup apart and reassembling the pieces. It doesn't make sense to me how this can happen either. But nevertheless, it has and did. I would trim a bit from the connection lines to the pump and reassemble. If that doesn't work, a new tube, then new pickup and discharge tubing. Last resort would be new roller assembly. Hopefully you can solve it before that last step as that is when it gets expensive.