AC66U rebooting randomly after connecting new Nvidia Shield TV Pro

I use my AC66U in AP mode as my main firewall/router is pfsense. I just got my new Nvidia Shield TV Pro 2019 and connected it to my AP's 5GHz Guest network (as my main 5GHz network is using a Radius server for authentication and the Shield does not support that). Everything seemed to be fine last night. When I woke up this morning, the AP is rebooting every 15-20 minutes or so. I've disconnected my Shield temporarily and the problem went away.

What could be causing this? I have IPv6...

AC66U rebooting randomly after connecting new Nvidia Shield TV Pro