Do you have a timer on the pump side or if the load comes live, its pumping its little heart out.

If the 2nd, then a 20w panel cant keep up. The controller is sensing low voltage in the battery and will not turn on the load. If you force the load on, the battery may not have enough juice to run the pump and just keep draining the battery.

If you add some sort timer that runs the pump for only 20-30 minutes in the morning. The solar panel has a chance to charge the battery the rest of the day.