New Digitizer is Black Screen, what other components could be failing?

UPDATE 2: I discovered that the usb board cable has a possible short. Either way, with just back cover off, if I apply slight pressure against the motherboard end of the cable, the display starts working, but only for a little while during boot. Any time the display begins failing as described, a couple minutes later, nothing turns it back on except a hard shutdown and reboot. I suppose I could replace the usb board again to be sure.

UPDATE: I tore down the N5 again and I replugged the battery and usb card cables into the motherboard. I did notice one of the antenna cables is broken now (another issue entirely). After doing this, while the back cover was still off, the display worked fine on boot. Once I replaced the back cover, the issue happened again. Black screen with an active backlight. The only two things I can think of that interface at the cover are the vibration unit and the NFC, neither of which sound like they'd impact display. (Side note, I have two back door covers, this issue occurs when I use either of them).

I have been forced to resurrect the Nexus 5 as my backup while I wait for an RMA on my primary.

Before I discontinued using the N5, I had replaced the digitizer (with housing assembly) only a few months prior. There were no cracks or any other indications of damage, but the display slowly started flickering and then turned black (the backlight was still on). Occasionally, when held at a seemingly random angle, the display would revive momentarily, only to switch to black again.

Now that I'm using the phone again, I bought yet another digitizer with housing assembly, and replaced the N5 components into that housing. The display worked beautifully, for about 2 hours. I was able to factory reset the N5 and get Nova Launcher and all my apps from my primary installed. I even went through all the updates to 6.0, including a couple security patches after that. But as soon as I even began moving it from its stationary position where it was getting charged/updated from my pc, I started having the exact same behavior as the last digitizer. Lines, occasional functionality at weird angles, black screen but backlight responds to power button, etc.

The closest related question I could find on this site only suggested looking for corrosion on the display connections. I see zero indication of any kind of damage or corrosion on the internals.

So is this goodbye? Or is there another component that I might check? I'm not keen to buy a new phone since I have an RMA out.