I second what I think Aleekat is talking about - the failure of the hybrid circuit that energizes the fuel pump while the engine is running.

Here are some questions:

Does the car start with starting fluid EVERY time? Did you try to starting fluid at a time when it cranked but did not start? Intermittent issues are difficult because they're not always there when we do diagnostic tests.

Did you jumper the fuel pump relay? Did that have any effect? Replacing the relay won't tell you if you have a failed ECU fuel pump energizing circuit.

I would do this, if you haven't already:
Find a time when it won't start. Then do both of these tests:

Try starting 1) with starting fluid 2) without and 3) with. That will sort of confirm that the problem was there during your test.

Jumper the fuel pump relay and RSR (just to be sure), then try starting. Swap the FI relay back in and try again. Then try each jumpered and FI relay again.

If I remember right, a lack of spark will prevent the ECU from turning on the FI relay. Making sure that you have spark regardless of the starting issue (the starting fluid test) before trying to diagnose something else that relies on it (fuel pump operation).

Good Luck! I hope you get this resolved soon.