X1 cable box connected with coax but doesn't work when router is in bridge mode

I have the Xfi system with three TV's.  Two of the TV's are wireless and one is connected to the coax coming into the house which is also connected to my Xfinity modem/router.  Everything has been working really well but I wanted to install a mesh network to get better connectivity, my basement workshop had really poor connection.  I bought the NEST wifi mesh system and got it all up and running, no issues.  Both wireless TV's work like a champ and I get great connections all over the house now.  But my one TV which is connected to the coax won't work.  It goes through the "connecting" screen saying "hi" in multiple languages and then gets to a Restart page with no other options.  I'm not sure why this box wouldn't work since it's hardwired and connected before the modem.  If I put my Xfinity router Bridge Mode disabled, the hardwired TV works fine.