Thanks for the detailed descriptions.
Regarding first meter:
Can you try updating the firmware from your friend’s iOS device? The update process only takes a minute from iOS and is generally more reliable than the Android update process. Your firmware on this meter is from January, the first release.
Regarding second meter:
You might be fighting two issues here. A little background: One thing I’m kicking myself over is that in bootloader mode, the microcontroller doesn’t enable low power, so it chews up power pretty quite fast (fresh batteries will die in about 1-2 weeks in this mode). On top of that the bootloader doesn’t check its own battery voltage, so one thing I’ve seen happen is that if you try to update firmware with batteries that are near death, the update will start but will fail partway through, resulting in an invalid firmware image, which then causes you to get stuck in bootloader mode. That might be what’s going on.
So for both meters, can you try putting in a fresh set of batteries and updating firmware from an iOS device? In theory the iOS and Android update processes are the same, it’s just there’s much less variation between iOS devices’ BLE implementations.
If this fails you can send your meters to me and I can reflash and recalibrate them manually.
Let me know how it goes, thanks!