Ausus AC68U Router & HG612 modem not working on BT Fibre 1

[Chissers]

Ausus AC68U Router & HG612 modem not working on BT Fibre 1
Router WAN won't connect to modem
I know the broadband is working because if I use my BT Smart Hub it connects and works perfectly.
I know the HG612 modem is working because if I use an external TP-Link Router it connects and works perfectly.
The Asus is running Asuswrt-Merlin, but my problem also exists with vanilla Asus firmware.
the combo had been working OK for many years previously.
Asus config:
WANport set to LAN4
PPPoE
Username: bthomehub@btbroadband.com
Password: bt
802.1Q VLAN: 101
get WAN IP automatically
MTU:1480 (also tried 1492)
The system log includes the following:

May 5 06:15:29 WAN_Connection: WAN(0) link up.
May 5 06:15:29 services: apply rules error(18475)
May 5 06:15:29 rc_service: wanduck 215:notify_rc restart_wan_if 0
May 5 06:15:30 pppd[431]: Unable to complete PPPoE Discovery
May 5 06:15:31 wsdd2[358]: error: wsdd-mcast-v4: wsd_send_soap_msg: send
May 5 06:15:33 pppd[1866]: pppd 2.4.7 started by *******, uid 0
May 5 06:15:38 WAN_Connection: Fail to connect with some issues.
May 5 06:15:39 services: apply rules error(18475)
May 5 06:15:44 services: apply rules error(18475)
May 5 06:15:49 services: apply rules error(18475)
pppd[422]: Unable to complete PPPoE Discovery
and then endlessly repeating:
services: apply rules error(18475)
pppd[431]: Timeout waiting for PADO packets

Any suggestions?
Thank you

[imjolly]

as all your testing seems to show the problem is with the Asus then maybe the Asus is now developed a fault.  Have you tried factory resetting the Asus?

[licquorice]

You don't need to set the vlan, that is a function of the modem.

[Chissers]

SOLVED!

Thank you!

I disabled 802.1Q ("VLAN101") in the WAN setting and normal service was immediately restored.