Port connection to XB8-T for external router

Question on which port to use for connecting an external router to my XB8-T modem/router...

I am using my XB8-T in Bridge mode with an external Gryphon router and have done so for several years.  I connect the Gryphon router to the XB8-T via Port 4, as per the provided instructions.  Very early Monday morning (sometime between 2AM - 3AM), my devices all disconnected and my Gryphon router went OFFLINE.  Upon investigation with Gryphon support, it seems that the connection to Port 1, not Port 4, was needed to get back online.  Mind you, it had been connected to Port 4 for YEARS without issue.  

So my question is which Port should I be using?  Did Xfinity load an update that disabled Port 4 for external router usage?  Any help will be appreciated, TIA.