CISCO Set top Box/DVR freezes after 9 seconds when using ORBI RBR750

[jr2021]

I am trying to set up my ORBI RBR750, and have an odd problem.
The internet connection and wireless is working fine. 
But, I have a CISCO ISB7150 set top box that is plugged into one of the LAN connectors on the ORBI router.  After resetting the set top box, a channel will play for ~9 seconds, and the image will freeze, shortly followed by a "lost connection" message.  If I change channels, the TV stream will start again, but again will freeze after ~9 seconds.    The freeze time is the same for regular and HD channels.
I am running the latest firmware.
I have rebooted/reset the router, Orbi satellite, and set top in various combinations, with no change.
I spent an hour or more with netgear support, where they suggested I change MTU and DNS settings, with no change.  They said they were not aware of an issue like this.
When I swap back to either of my old TP Link routers, the problem goes away, and the TV works fine. 
I currently have a TP Link router (with the wireless disabled) connected to the modem, with the set top box connected to it, and it works fine.  I then have the ORBI plugged into a LAN output of the TP Link, and am using the ORBI for mesh wireless.  It works, but I'm annoyed that I need to use 2 routers.

Does anyone have any suggestions of a possible fix for this? 

[CrimpOn]

Page 74 of the Orbi user manual talks about IPTV:

https://www.downloads.netgear.com/files/GDC/RBK752/RBK752_UM_EN.pdf 

(Don't know if this applies in your situation, but ........)

You might consider putting the Cisco box in the Orbi DMZ, which gives it direct access to the internet.

[jr2021]

Crimpon:  Thanks, I looked at the VLAN/bridge settings that you pointed me to.
I enabled the VLAN/bridge "by bridge group", and enabled ports 1 and 2 on the Orbi router.  I plugged my Set top box into Port 1, and the DVR wireless access point into port 2, and the TV works for both the main and remote DVR/TV.
As I understand the (vague) documentation, the Set top box is now bypassing the router's NAT.  Hopefully this is also isolated from the other devices on my network, so it won't be a vulnerability.

But, this only works with wired ports, and this prevents me from doing one of the things I'd hope to do with the upgrade to the Orbi, which is to move the DVR wireless access point to the Orbi sattelite to get it closer to my remote DVR/TV.  I see the option for setting up the VLAN/Bridge by "VLAN tag group", but I am having trouble figuring out how to add a wireless node to the group.  Again, the documentation is not great. 

So, for now, this is a partially solved problem.  Thanks for your help.

[jr2021]

Update:  it worked for a while, but upon a reboot, the Orbi would not connect to the Modem and external internet.  When I disabled the VLAN/Bridge, it reconnects to the Internet.  But I lose the TV connection again.  Sigh.

Looks like the Orbi is just not compatible for some reason.