RBK353 (RBR350 / RBS350) unstable wireless backhaul

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?

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.
https://kb.netgear.com/31029/Where-should-I-place-my-Orbi-satellite 📡

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

Set 20/40Mhz Coexistence to 40Mhz only. Set CTS to 2347. Save settings and reboot the router and satellite(s). Under Advanced Tab/Advanced Settings/Wireless Settings

Is Armor or IPv6 enabled? 

Netgear has set up a community forum specifically for the Orbi AX products. Most of the people who watch that forum are more likely to have experience with Orbi AX (WiFi6 RBK 3,7,8 and 9 Series) products. Might be more likely to find someone who has a solution if the question is posted there:
https://community.netgear.com/t5/Orbi-AX/bd-p/en-home-orbi-ax

Please use this link to the main forum product list to review and choose where to make your posts. 
https://community.netgear.com/t5/NETGEAR-Forum/ct-p/en-netgear