Tasmota on Sonoff Zigbee Bridge - Unable to flash zigbee module

I am following the instructions here to flash my Sonoff Zigbee Bridge with Tasmota: Sonoff Zigbee Bridge ZBBridge Zigbee compatibility

Everything goes fine until I get to the part where I flash the zigbee module. I perform the firmware upgrade procedure using the required .ota file (in this case version 6.7.9, though I have tried multiple) but the upgrade gets stuck at “Upload Transfer” and goes no further than this. In the console output I see:

18:22:26.102 UPL: Transfer 192240 bytes
18:22:26.102 UPL: Successful 192240 bytes
18:22:26.114 HTP: Upload transfer

But it gets stuck there and goes no further. I have rebooted and redownloaded the files many times and used different client machines but nothing seems to work. Does anyone know what I am doing wrong?