So here’s an interesting new development. I went to turn off my OSSC, and flipping the on/off switch did nothing. I then unplugged the power supply (official power supply, purchased with the OSSC), and the screen flickered a bit, but stayed powered on. I then unplugged the HDMI cable, and it powered off. I plugged the HDMI cable back in, and the OSSC was again getting power. I tested the OSSC quickly, and it seems to be working fine in this powered-by-HDMI state.
Well I figured out the general cause for the issue, although am still not clear on the exact cause. I moved some cables around amongst the various splitters and switchers I have in my a/v i/o chain. I had somehow achieved what I was trying to do, but by connecting cables in a different configuration than I thought I had. I believe the OSSC HDMI out was simultaneously connected in the chain as an input and an output. Not sure how that would result in the device being powered via its HDMI output…if someone has a detailed explanation, I am interested to know.