I was just about to try flash it. I managed to fix it by opening it up, connecting the 3v3, gnd and then power cycling very rapidly (10 times in a few seconds)
Then the blue light started flashing momentarily and eventually went solid indicating it was alive again.
I have the same problem. Can’t be sure it was out of the blue. I did flash tasmota and the zigbee firmware. It was working. I was getting zigbee message through ZHA. Then upon reboot it seems to be bricked. Can’t reflash. And no serial communication via putty. Just the solid blue light on power up.