Welp, as embarrasing as it is for me to admit this, it was a power problem. I got a different charging brick and cable on a whim to try it out and it all runs fine. So I'll post this here for posterity, even though I'm sure you've probably posted it may times before: try multiple power chords and power bricks if you're using the USB-C port for powering your OPI 3 LTS (and probably other boards)!