@Riley_S 

Don't see a "ver" or "version" on the label.  There is a US/1.6 on the label so, maybe version 6?

I have two Decos.  Operation Mode is set to Wi-Fi Router (not Access Point).

The network configuration is as so (dashes equal Ethernet CAT8 cables):

AT&T Fiber Optic Modem-----Motorola BGW210-700 DSL UVerse Router in Pass-through mode-------(2.5GB)Main Deco(10GB)------(10GB)Satellite Deco

The other 10GB Main Deco Port goes to a ProSafe XS505M 10GB Router that then goes to the 10GB port of a TPLink TLS63428X Router.  The TPLink TLS63428X router has 16 of its 1GB ports going to various devices, including a PC where I accessed the main Deco's IP address in an attempt to get the client list.

The Decos are acting as the DHCP server that gives out IP addresses.  The Decos have WiFi enabled and are broadcasting 2.4, 5, and 6 GHz SSID's.  MLO is disabled.

As to your questions:

1. When a new device connects, does the client list update - just placing the device in the wrong category(online/offline)?

I just set my phone to randomized MAC to simulate a new device and connected.  I got a new IPA, but the device is not listed in the client list anywhere (can't find IPA or new radomized MAC address).

2. "A Device Reboot Will Refresh the List" - Rebooting the Router, or the Client Device? This will cause the device to then appear in the Online Category?

A Deco Router reboot will update the client list that can be accessed through the Deco App.  A client device reboot has no effect.  I only have to reboot the main.  Yes, the new device will then appear in the client list as on line and with the correct information (IPA, network connection, MAC address, etc.).

3. When a device disconnects from the network, does the client list update?

So, I'm not sure and I just rebooted the router to answer question 2, so the list is no longer frozen and working on the App and through the web interface. Next time it freezes I'll check.

4.Does the behavior remain the same with both wired and wireless client connections?

Same answer for number 3.  I should have checked this before rebooting.  Next time it freezes I'll check.

5. Will completely closing out of the Deco App refresh the client list when reopened?

No.  Closing the app has no effect.  Likewise clearing the cache has no effect.

  @Riley_S So, I've given it a while and installed an update.  The issue has not reappeared.  I'm going to put this is in the "fixed" category.