EX6150v2 - Client LED - Losing Wireless Connectivity

I have an EX6150v2 Range Extender, in extender mode paired up to an Arris (Motorola) Wireless Cable Modem. I have setup the range extender according to the instructions (extending both the 2.4G and 5G bands).

Initially it seems to work and both extended networks appear to work fine - but after about a half hour, they are still visible to my devices (Windows laptop, Apple TV and iPhone), but no longer connect to the internet, and the Client LED light is dark.

I have tried repositioning the extender to be closer to the router - but it still doesn't work after a short period. At this point my extender is less than 10 feet from the router in clear line of sight.

Any suggestions?