RBK50 with Xfinity modem/router

I am installing a new Orbi RBK50 with satellite, plus a wall satellite and outdoor satellite from an old system.  I have Gig speed internet from Xfinity.  I put the Xfinity modem into bridge mode, then called Xfinity because they have to do some magic on their end because I had some Xfinity Pod extenders in the house.  With that done, I set up the Orbi, then rebooted everything from the modem to the router, to the switches, then devices.  Everything was fine at first, with all devices being assigned an expected 192.168.1.x IP address.  But then I started getting random devices assigned a 10.0.0.x IP address, like the router wasn't even there so they were defaulting to the modem, which, as I understand it, shouldn't have been giving out any addresses at all.  Any device assigned a 10.x address could not see the internet.  Anything with a 192.x gets internet just fine.

I rebooted everything again, and had a whole different set of devices assigned to 10.x, with some still assigned 192.x and working fine.  It is a combination of wired and wireless devices that get the 10.x addresses, and different every time I reboot, and sometimes randomly switching from 192 to 10 after running fine for a while.

I'm about at my wit's end on this.  I'm still renting a modem from Comcast because my phone comes from Comcast through the modem (lousy cell service where I live).

I would really appreciate any thoughts on this.  The XFi extender pods just don't reach far enough, so I really need the Orbi system to be up and running.