Comment by kijin
I once managed to brick a PC motherboard that advertised "dual BIOS". It didn't fallback to the previous version after a botched BIOS update.
It's totally possible that the update corrupted the other bootslot as well. If those blocks aren't off-limits to the updater program, it's just an off-by-one error waiting to happen. Slot 0 or slot 1?
Another possibility is that the updated version booted up just enough not to trigger the automatic fallback, and then got stuck in a loop.