Download speeds at 1/10th non-Orbi Wifi router since latest firmware

[jcricket73]

I had to replace a totally dead 2-month RBR50 (no amount of rebooting/factory resetting fixed anything). New RBR50 and 2 satellites arrive and get installed, all the connections work ok (can connect to the wifi, finds the satellites, etc) - but speed is 1/10th of what I'm getting if I connect to to the Orbi vs the modem/router from my cable company.

IOW - if I connect to Comcast's xb6 over wifi I get like 500Mbps (I've used Speedtest, etc) but if I connect to the Orbi (router or satellites) I get at best 50Mbps.

I've tried connecting over Ethernet, factory resetting, rebooting, etc. I saw a couple other folks saying the latest firmware might have caused this. I tried to downgrade, but it actually updated the firmware on the satellites back to the latest version before I could get to the router (LOL).

I don't even know what to do, I am about to chuck these into the sea, it's far worse than the janky Comcast router + standalone access point I used to have. 

Any ideas before I give up and return these?

[FURRYe38]

What Firmware is currently loaded?
What is the Mfr and model# of the ISP modem the NG router is connected too?

Modem Combo Units:
This would be a double NAT condition which isn't recommended. https://kb.netgear.com/30186/What-is-Double-NAT
https://kb.netgear.com/30187/How-to-fix-issues-with-Double-NAT
Couple of options,
1. Configure the modem for transparent bridge or modem only mode. Then use the Orbi router in router mode. You'll need to contact the ISP for help and information in regards to the modem being bridged correctly.
2. If you can't bridge the modem, disable ALL wifi radios on the modem, configure the modems DMZ/ExposedHost or IP Pass-Through for the IP address the Orbi router gets from the modem. Then you can use the Orbi router in Router mode.
3. Or disable all wifi radios on the modem and connect the Orbi router to the modem, configure AP mode on the Orbi router. https://kb.netgear.com/31218/How-do-I-configure-my-Orbi-router-to-act-as-an-access-point and https://www.youtube.com/watch?v=H7LOcJ8GdDo&app=desktop