VPN problem with XB6 modem

[#1]

Here is the situation,

A,B,C are three different SHAW internet CX,

A is fiber internet cx, setup VPN on his own router, testing pass;

B is using modem Hitron CGNM-2250, using VPN without any problem when connect to home wifi;

C is using modem XB6, got error message when trying to connect VPN; Screenshot attached.

At the same time, VPN works with other WIFI.

I don't find any settings in XB6, and still got the same issue even disabling firewall in XB6

It seems that XB6 is blocking VPN.

[#2]

Can you try with the XB6 in bridge mode?  Either directly connected to your computer or with your own router?

[#3]

I did, it works in bridge mode. 

[ducktour]

Anyone find a fix for this?  I enabled bridge mode and the VPN connected and verified OK.  In normal mode I connect but user profiles will not verify.  I suspect the modem does not support GRE.

Bridge mode is OK but I was not popular with the family as it shuts down the modem functions.