Well I took my trusty USB microscope to the MPU9050, the tiny QFN that's been problematic on some Crazyflie 2.0 builds, and noticed a lack of fillets on the edges of the QFN pads. I had a "it's a UNIX system, I know this" moment from all the QFN soldering on my Tiny Bit Dingus project.
I put a little flux on the edges of the package, a little solder on my iron's chisel tip, and went around slowly heating the pins. Using flux with this kind of rework is misleading since it's hard to see the joint until you clean it off. But after cleaning and a check for shorts it booted right up with the entire IMU responding.
I assembled the rest of the quad, balanced the props while the battery took its first charge, and stayed up way too late playing.