So, if I solve the problem without shipping the GF+ back, what do I win?
tldr Solution: ribbon cable connecting the lid to the main case was loose on the case’s end (as opposed to lid’s end). Here’s some pics of the problematic connection – it’s where the ribbon connects to the white PCB:
Slightly longer explanation: Was thinking more about the symptoms and how the LED lights were acting irregularly and how the lid opening distance was affecting whether I ended up in scanning spiral of doom. My sense was it had to be a cable or connection related to the lid’s hinge. Last night, I was poking around the end of the ribbon where it connects to the lid, but it was definitely a tight connection. For whatever reason, it didn’t occur to me to check the other end where it’s mounted to the back case. Today, I was walking by and on a whim, decided to open the lid and have another look in the daylight. The ribbon connector looked perfectly fine, but when I gently touched it, it was clear the connection wasn’t snapped shut. (I have some passing familiarity with these types of connections – when replacing the battery in my Nexus phone, I had to disconnected/reconnect several of these hinged mechanisms to finish the job.) Anyway, I snapped the ribbon hinge closed, booted the machine, pulled up the app, and checked to see if the problem had been resolved. It had. Hoo-ray!