Orbi RBK852 suddenly dropping internet connection

IF the front is turning PINK this usually means the RBR has lost internet services with the ISP modem or the modem isn't give good services to the RBR. 

Have the ISP ensure that the modem is getting good signal online the line from the ISP. 

Have the ISP check the signal and line quality UP to the modem. Be sure the ISP provisions the modem correctly.
Be sure there are no coax cable line splitters in the between the modem and ISP service box. 
Be sure your using good quality RG6 coax cable up to the modem. 
Be sure to power OFF the modem for 1 minute then back ON.

https://www.duckware.com/tech/solving-intermittent-cable-modem-issues.html

Be sure your using a good quality LAN cable between the modem and router. CAT6 is recommended.

What is the size of your home? Sq Ft?

25ft is too close between the RBR and RBS. 30 feet or more is recommended. 

You may want to update FW on the RBS first, then RBR lastly:

https://community.netgear.com/t5/Orbi-WiFi-6-AX-and-WiFi-6E-AXE/New-RBR850-RBS850-Firmware-Version-4-6-8-5-Released/td-p/2234046/jump-to/first-unread-message