I don't know if you had any guidance from customer support, so I'll ask a few questions:
When you did the RF/HW loopback, did you mute the far end unit? (The RF/HW loopback should be performed in "isolation" with all other link components muted.)
Again, what's your grounding and surge suppression look like? (Links with grounding or surge suppression issues can be flaky at times.)
Are you using PoE or a separate DC feed? What made you think that the power supply might be at fault?
None of my questions are meant to be critical; I'm just curious. Thank you for posting your results. I'm sorry you're having problems with your link!
Dave