Intermittent starting problems when the car is hot

I ti has done it four time, it alwways starts with multiple attempts after about 20 minutes. Usually I ahve called a tow truck and I have to call them back becuse it finnaly catches and starts. The battery and starter seem to be fine. The mechanics have not been able to read out any CODES, they replaced the Fuel Injector relay, just because it was the cheapest think to fire a shot in the dark. I think the car is still in great shape but, I am now afraid to trust it. I can't get it to repeat this process while at the repair shop, it seeems to be fuel related, but I could be wrong. I can't recreate the exact conditions to make it happen. When it does it, I keep trying it every few minutes and it always sounds as though it very much wants to start, but can't quite get enough gas. And then just like that it starts up runs fine for a period of time, no stalling, no rough idling, purely a start issue, after driving for a while and shutting down the engine. Would love some insight. Thanks