Loosing prime in half an hour

[Allwash]

I’ve been fighting this for a while now and I give up trying to figure it out myself. What happens is the pump runs perfectly fine but when it sits idle for about half hour give or take it runs dry for like 10 seconds and starts working normally again. It has a brand new check valves that I tested to make sure it’s working properly. There’s no leaks that I can see and I haven’t seen any water dripping on the ground. I blew air into the line with the ball valve closed on the bottom of the tank and it held pressure just fine so I just wanted to ask why does it keep losing its prime? The water below it was from me taking it all apart to thread tape all the fittings again. With how it runs dry it’s already starting to cause damage to the seals on it so that’s why I want to figure this out before I put new seals in and thanks for any help