Zone needs to run twice in a row to achieve proper pressure.

I’m stumped. Starting about two weeks ago, our sprinkler zone needs to run twice through the controller to achieve proper pressure. The system works fine if I manually turn the solenoid. I’ve replaced the solenoid, the diaphragm, swapped wires with a different zone and tried a different zone on the controller. Flushed the valve. All our other zones (1 sprinkler, 3 drips) appear to be working fine.

Any ideas what it could be? Do I need to replace the entire valve?