FVS318N firewall/router/switch/Wi-Fi keeps disconnecting from available Internet service at midnight

Thanks for the earlier reply, John. I immediatly started working on a response, but since my "issues" only happen around midnight, I can only observe the effect of any adjustments once a day and for a limited time late at night. These conditions make for slow feedback.

To reply to the request as to what is connected to the router, here is a description: The router with its internal switch and three external unmanaged switches usually has around 33 devices connected, most of which are both hard-wired and fixed local IP connections. These include a printer, two (sometimes three) web-controlled power distribution units (PDUs), 20 IP cameras, three desktop computers (one is an FTP server for the cameras), a Silicon Dust Broadcast TV to LAN-only video streamer, and an external 2.4Gig N access point which hosts the only DHCP devices. Until lately, I have not used the internal access point. From the access point, DHCP devices include a Honeywell thermostat (smartphone cloud app), a WAN video streamer (Vulcano), a gateway or hub for several Z-wave devices (smartphone cloud apps), and occasional connects of smart phones, tablets, and notebooks.

The router config is customized to allow remote access to most of the hard-wire fixed IP attached devices similar to the FVS318v2 and FVS318 I used for years before getting the FVS318N a few months ago. Under the security/services menu, I define 60 individual ports to open, and under Security/Firewall, I currently have 29 of those services enabled and mapped to fixed Local IP hard-wired ports. These rules allow for remote access to each of the IP cameras, the FTP server (for the cameras), the PDUs, and ports for occasional remote desktop protocol (RDP) access to the other desktop comptuers. I created these rules from scratch, I didn't import them from prior, similar-model router config files, although to the best of my knowledge, they exactly replicate the prior rules. 

The only apparent problem is that at midnight, available Internet access is routinely dropped. Power cycling the router brings back Internet access briefly, then it drops again. This happens over and over again. Eventually, I have to sleep. When I awake at daylight, everything is working fine and continues to work just fine all day. Frustrating. What is it that causes problems to only occur at midnight? I've never established session limits or any schedule for any operation. Similar custom rules worked for maybe up to 10 years with the for two prior versions of the router. Why not now? 

To resume troubleshooting a few days ago, I relocated the router so I could easily observe the status lights. As suggested in your original response to my post, I disconnected all wiring from the switch ports, and restored the default configuration. To my suprise, the router didn't drop off line at midnight. The next morning, I restored the old setup so I could normally use the system during the daytime.

The next night around 11PM, I restored the default, changed the default LAN from 192.168.1.1 to 192.168.102.1, changed DHCP from the default range from 10-255 to 201-255, established a custom access password, disconnected all wires to the internal switch, enabled the inboard access point, modified the SSID and enabled encryption so as to mimic the outboard access point, set local time to Z-6 with DST, changed DNS for the service provider defaults to the Open DNS addresses, saved the configuration, and rebooted. At midnight, with only 3-4 Wi-Fi devices connected via DHCP, the Internet connection stayed online for a pleasent change. The next morning, I restored the old setup and plugged in the external switches so I could normally use the system during the daytime.

The next night around 11PM, I restored the config from the night before which, as normal, triggered a reboot. Then I connected only the most critical external switch (Netgear 24 port, most of the ports are used). At that point, with the significant exception of no ability to remotely access any device, I restored local connectivity to the hard-wired local fixed-IP devices such as the cameras, PDUs, and desktop computers; plus the Wi-Fi connected devices as well. I watched the router at midnight, and it stayed online. I saved this second "new" configuration. The next morning, I restored the old setup so I could normally use the system during the daytime.

The next night around 11PM, it occurred to me that the latest "new" configuration was apparently equivilant to old configuration if none of the custom services were enabled in the firewall. So, I went to the Security/Firewall menu, disabled all the custom services, rebooted, then waited and watched. At midnight, all the router lights went out and it went through a uncommanded reboot. Internet connected briefly, then was lost. I powered cyled the router denying power for about 30 seconds. After it rebooted, Internet came back for a few minutes then dropped off. Apparently, even though no custom services were enabled, there is something in the old configuration that is making the router significantly misbehave.

This morning, I have restored the old configuration because remote access is needed. As usual, everything works fine as it always has during the day. Tonight, around 11PM, I plan to restore the latest "new" configuration which has no custom services defined or enabled that would open external WAN ports in the 10xxx range then map them to port 80 or 21 or 3389 on fixed internal LAN ports, then watch what (if anything) happens at midnight. After a few nights observing whether the new config is stable, I'll start defining and enabling a few port forwarding rules and observe what happens at midnight.

I'm frustrated at the time expended for such slow-motion troubleshooting, but I don't seem to have much choice.