Sonoff Zigbee bridge repurposing to router doing strange things

I used to use a tasmota flashed Sonoff Zigbee bridge for my initial Zigbee network. I then replaced it recently with the Sonoff Zigbee 3.0 Dongle. Everything has been working great, until the other day I saw the old bridge laying around and remembered that it could be used as a zigbee router. I found Digiblurs docs for doing that and followed those through:-

When it found the bridge I renamed it and went to my devices. I could see it, but it had replaced my USB stick in the network. After a while I realised the USB stick was still the USB stick, it had been the device that was found that I renamed.

Every time I follow the instructions through and put the bridge in discovery mode, what I find is actually the USB stick plugged into the box. The reconfigured bridge does not appear. I wondered if there was something about the firmware and a zigbee version of a mac address in that causing this. Has anyone encountered this or got any ideas?