DHCP issues on RBR350

Thank you for your reply. I will answer your questions

What Firmware version is currently loaded?

As mentioned, the latest - V4.4.1.29_3.10.80

What is the Mfr and model# of the Internet Service Providers modem/ONT the NG router is connected too?
Be sure your using a good quality LAN cable between the modem and router. CAT6 is recommended. 

It is an o2 own branded 5G router, made by ZTE. It has built in Wi-Fi which is switched off, and DHCP switched off. It is connected to the WAN port and in a different subnet. Issues I have had in the past were the same with the modem connected or disconnected.

What is the size of your home? Sq Ft?

around 2000

What is the distance between the router and satellite(s)? 30 feet or more is recommended in between RBR and RBS

to begin with depending upon building materials when wirelessly connected.

its greater than 30 feet in a diagonal straight line to both. across floors and even in a different building in the case of the wired one.

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What channels are you using? Auto? Try Auto and 48 on 5Ghz. Or try setting manual channel 1, 6 or 11 on 2.4Ghz and 40 to 48 channel on 5Ghz.

I have been on auto for 2.4 GHz, setting of  5GHz channel is greyed out, assume because I'm in Europe. Its set to 108(DFS) and I cannot change it. I have changed 2.4 GHz to chan 6 as per your recommendation.

Any Wifi Neighbors near by? If so, how many?

1 or 2, very low power in my house, around -90dBm 

Set 20/40Mhz Coexistence to 40Mhz only. Save settings and reboot the router and satellite(s). Under Advanced Tab/Advanced Settings/Wireless Settings

Done, but if there are settings that cannot be used then this is a bug.

Has a power off for 1 minute then back ON with the ISP modem and router been performed since last update?

Yes, multiple times

Be sure to restart your network in this sequence:
Turn off and unplug modem.
Turn off router and computers.
Plug in and turn on modem. Wait 2 minutes for it to connect.
Turn on the router and wait 2 minutes for it to connect.
Turn on computers and rest of network.

I think this is unnecessary, given the circumstances of my issue. Things have been working for weeks after my last changes to the Tasmota devices to static IP. Given a reboot solely of the RBR350 fixed a stable problem then I don't think my issue is related to power up sequence. Also, I don't expect a high quality router, the cost of the Orbi to be sensitive to this. If I have a power cut or breaker trip, I am not going to religiously follow a strict power up sequence every time. If the Orbi is sensitive to this I might as well throw it in the trash.

Has a factory reset and setup from scratch been performed since last FW update? A complete pull of the power adapters for a period of time after the factory reset then walk thru the setup wizard and setup from scratch.

Yes, multiple times

Recommend setting the default DHCP IP address pool range to the following after applying and a factory reset: 192.168.#.100 to 192.168.#.200.

Its set to 192.168.200.2 to 192.168.200.199. My static IPs are set to 200+. I don't want to change this unless absolutely necessary. Again, if settings here are not settable to what the user wants, this is a SW bug and needs to be fixed.

I would power OFF the ISP modem for 1 minute. Factory reset the Orbi router and power it off. Power ON the ISP modem and let it sync. Then power ON the Orbi router and walk thru the setup wizard again using a wired PC and a web browser.
Press the back reset button for 15 seconds then release. 

I factory reset the router multiple times during my investigations. Problems arising weeks after initial setup I don't believe are related to power up sequences prior to it.