I have the same problem with BT Hub Business Hub 5 and Zyxel NBG4606 or EDIMAX BR-6574n.
Maybe someone help us?
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EDIT:
[b]dassa[/b], do you use a Openreach modem [white device]?
When I remove the Openreach modem from my network the BRIDGING work fine with Zyxel and Edimax routers.
Maybe you need remove the Openreach modem from your network?
Sorry for my English.