Then, after checking for any leaks, I'd pop the top off the valve and make sure the line is clear. A rock could have lodged in there or if a PVC repair was done there could be a chunk of dried glue blocking the passage.

Is that zone built with PVC pipe or poly pipe? If poly pipe, there's a chance it got kinked somewhere or a tree root is pinching it somewhere, but this is less likely than all the other possibilities.