Hi, is it possible that the non-return valve has blocked and damaged the pump? I agree you should try swapping the pump with one of the others and without the non-return valve to see if that works. If so, it looks like you'll need a new pump and non-return valve.
Your not alone with this, I just got home from a drive and I've got no screen wash to the rear now. Must have been due to the lockdown lack of use. What fun.
Let us know what you find.
Tricky.