I've been so busy with other projects that I'm just now getting around to writing this up. This problem has been occurring for about a month and a half at least.
Shield is running v1.51 SP1 and is setup as a router. The entire system is pretty basic, I'm only assigning IP address based on MAC address so that I can follow who is who on the home network. I've suppressed all notifications in the Log under Intrusion Prevention till I get this issue under control... one less thing to deal with at the moment.
Each day at 3:48am (about) just after Shield updates all access to the internet stops for all devices connected to the LAN. No amount of time after the update seems to make a difference. Eventually I do a Manual Update or Reboot.
Logging into Shield the Status/Overview screen shows the date and time the update completed at roughly the time mentioned above. Once or twice I've noticed the “Unsaved Changes” notice in place, most of the time this is not the case.
Under Network/Diagnostics I can Ping and/or Traceroute any site I want on the internet. Everything seems to be OK internally. Shield sees the outside world.
I've found that the easiest and fast way to get connectivity back is to do a manual update at Status/Itus Settings/Update Shield, followed by a “Save and Apply Changes” when the update is complete. Entirely rebooting Shield also works but takes much longer.
I thought I might just do a factory reset but thought again that maybe I had run into a bug that no one else has seen and wanted to save the state just in case.