PepWave SURFSOHO not connecting on BT Infinity


I have a ongoing problem whereby connecting to the internet by WiFi slows down significantly and then browser access to the management interface of the Surf SOHO is locked out.

If I power down the router then when it reboots, I can access the management interface but the router doesn’t connect to the BT Infinity service. I’m using a TP link basic router configured as a pass through VDSL modem to connect the Surf Soho to the BT service.

If I disconnect the Surf Soho and the TP link and replace them with a BT Home hub it connects immediately.

If I leave the BT router connected for 24 hours and then replace with the Surf SoHo and the TP Link then the connection is made within 5 minutes.

I have tried both Netgear and TP Link basic routers configured as pass through modems and the problem is the same.

Any suggestions?