My Orbi RBR750 router stopped connecting to the internet

What Firmware version is currently loaded?
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. 

How many RBS are deployed? 
What is the size of your home? Sq Ft?
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.

Does this happen with the RBS turned OFF? 
Does this happen with both wireless and wired devices? 
What channel configurations are currently set on the router?  

Whom ever told you to never factory reset told you false information. FR are a last resort or can be used to troubleshoot problems and DO NOT damage the HW. 

Factory reset and setup from scratch :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 with a wired PC and web browser. 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.
https://kb.netgear.com/24089/How-do-I-specify-the-pool-of-IP-addresses-assigned-by-my-Nighthawk-router
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. 
https://kb.netgear.com/31486/How-do-I-reset-my-Orbi-system-to-factory-default-settings

OR if you have access to the RBRs web page, I prefer doing a FR using the ERASE button:

https://kb.netgear.com/000062081/How-do-I-erase-the-configuration-settings-on-my-Orbi-WiFi-System