RBK50 repeatedly dropped internet after Firmware update a few days ago

[lwhi021]

My Orbi is connected to a Huawei HG659 modem wifi on that is off and all device connections and DHCP allocation are via the Orbi. I have had the system for some time now and it has been relaible and stable.

After a firmware update a few days ago I kept loosing my internet connection which I deduced was a result of the DNS server settings getting corrupted in the HG659 modem.

I spent 2 very frustrating days trying various things to get my system stable again. Ultimately I think I stumbled on the solution by accident. I plugged my laptop in to the HG659 after the internet connection failed  as I wanted to check the settings on the HG659. To my surprise the internet connection started to work again. I think that by having an internet connected device attached directly  to the HG659 it is able to manitain that connection properly. I subsequently connected a TV set top box to the HG659 and have not had a problem since. 

While I believe I no longer have a problem I don't understand the technicalities that may be behind the original problem

[FURRYe38]

What Firmware version is currently loaded?

If your modem has a built in router and wifi, This would be a double NAT (two router) 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 

Try option #2 first, or #3...

[vajim]

Your answer is in your subject line

RBK50 repeatedly dropped internet after Firmware update a few days ago