Orbi RBRE960E not renewing/releasing DHCP assigned by ISP - causing internet to go offline

Does the front LED on the RBR turn PINK when this happens? 

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. CAT6A STP is recommended. 

v.31 had problems reported from posters. I recommend updating to more newer code: https://community.netgear.com/t5/Orbi-WIFI-6-AX-AND-Wi-Fi-6E-AXE/New-Orbi-RBR-RBS-850-860-and-960-series-Firmware-Version-7-2-7/td-p/2435724

If you do update, I highly recommend doing a power OFF of the Orbi system and your ISP modem/ONT for 1 minute then back ON. 

I would get with the ISP and ask them if there seeing any interruptions on the ISP Modem/ONT during these time frames to help see if they can stop these interruptions from there side.