My experiments:
Attached a load that pulls ~0.8A on the I2C 2 port. Ran trials that consist of powering the Cube Black, waiting ~5 minutes for the current to be limited (or not), then un-power the Cube.
Copter 3.5.7 NuttX: Problem appeared 37/50 trials.
Copter 3.6.2 ChibiOS (and later): 0/30 trials.
Copter 3.6.8 with above PR: 0/10 trials.
It seems that, at least for this specimen, the problem had already been solved by Copter 3.6.x, I guess it gets hidden by different timing on ChibiOS boot, so I can’t really test the PR with this particular Cube. We have blue cubes on hand, I’ll see if I can reproduce it with them.
To me, the mystery is why this suddenly started happening. We’ve flown 3.5.7 since its release and only had this issue appear lately, which suggests a hardware change. It won’t be an issue once we finish migrating to 3.6 (assuming the PR fixes it), but the sudden and inexplicable onset was a bit jarring. Glad @Morso was able to dive into it deeper than I could.