In this case even after changing channel for 5G network if the issue persist please try using different channel and monitor connection and if still issue persist then we need to check the cable signal level on the modem interface to proceed further on this case. so please follow the instruction on the below link.

http://arris.force.com/consumers/articles/General_FAQs/G34-G36-Cable-Signal-Levels

Hi - the issue persists. I’ve also tried factory resetting the device. In completing the instructions linked, it looks like the Upstream Transmit Power Level may be too low. How do I resolve?

If this requires outreach to my internet service provider, can you please provide me specific instructions that I can relay to them?

41 upstream is not too low. Isp can put a attenuation filter in line to kick it up to 50, but I suspect you're experiencing an issue like I am with your gateway. Poor signal will affect overall performance but not specifically target an antennas broadcast. However, when I'm disconnected from the 5ghz on a device, it seems my Arris is not working period. Wired etherner and wifi. Seems more hardware related

I'm having the exact same problem with the exact same router and isp as the op. It has been happening for about a month but I've had the router for a few months. The 5ghz drops several times a day and only restores if the router is reset. The 2.4 works fine. I've contacted Xfinity and they have said it's a hardware issue.

Same issue here with my new G36, anyone has solutions other than resetting it everyday?

Are you familiar with the gui? 192.168.0.1? I set mine to bridge mode in that gui and I'm using a nighthawk as the router.. 3 days strong no interruptions knock on wood

@SURFboard Moderator - any thoughts on how to resolve? Looks like this is a reoccurring issue for others as well. Thanks for your help!

It's a hardware issue