RBR50 keeps hanging

What mode is the ISP modem in? If router, the Wifi radios on this modem should be fully turned OFF. Full bridge mode is recommended on the modem however. 

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#1 first if possible. Then try #2...

If you turn OFF the RBS and leave just the RBR online. Does the RBR hang or experience this issue. 

Do both wireless and wired devices stop betting internet services when this happens? 

Does the RBR show any top ring light when then happens? 

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