I wanted to share this in case it helps someone else.
My WHOOP MG basically looked bricked after a firmware update. It was still showing up over Bluetooth, and I could even read the battery level and device info, but the green sensors on the bottom never turned on and it would not work normally in the WHOOP app. So it felt like one part of the device was alive, but the actual sensor side was frozen.
Support sent me a replacement, but before giving up on the old one I decided to keep testing it. Since it was still visible over BLE, I tried connecting to it over and over from my Mac with a small Python script. The script kept scanning, connecting, reading battery/device info, disconnecting, and repeating. The idea was just to drain it faster and force a real shutdown.
That ended up taking a while, but once the battery finally hit 0%, the band fully died. After that I put it on the charger, it rebooted, and to my surprise it started working again.
So in my case, the thing that fixed it was not reconnecting, not random BLE commands, and not anything inside the app — it was letting it fully discharge until it shut off for real. It seems like the update left it in some half-broken state, and a true full power loss reset it.
I cannot promise this will work for everyone, but if your WHOOP MG still shows up over Bluetooth and still reports battery info, it might be worth trying before throwing it away. I would still be careful, and obviously do it at your own risk.
If anyone wants, I can share the simple Mac/Python script I used to speed up the battery drain.