Packet loss every 24 hrs and 1 minute

Are you using a third-party router with the AT&T Gateway in IP/Passthrough mode?

That sure looks like a DHCP Renewal cycle timeout. DHCP lease renewal requests should start at 1/2 the lease period but not all clients play nice so the DHCP Sever will force renewal at the time specified in the Server configuration.What do you have set for your DHCP Server Lease renewal period on your AT&T Gateway?

Here is an example of the settings page from a BGW320 Gateway: http://192.168.1.254/cgi-bin/dhcpserver.ha

ETA: Additional DHCP comments...

Dave

Correct, have a Unifi Dream machine with Passthrough set. 

And yes, it has a DHCP lease renewal set for 1 day. I've just increased it to 99 days. see if that makes a difference. \\

This is the first time I've seen the Dream Machine not play nice with lease renewals. 

If you have IP Passthrough set, the DHCP lease timer is on the IP Passthrough page, make sure you have that one set correctly and make sure your UDM is actually getting the Public IP set for its WAN.

No joy guys. 

Lease changed for Passthrough as well. 

Do the router logs on your router give any indication of an issue and what that issue might be at the time of loss of Internet?