Thanks itman and The Pit.
The network consists of a Netgear R7000 router and a Netgear EX7000 mesh extender running both a 2.4 and 5G network with one wired desktop which never duplicated) and 15 devices.
Here's the solution:
1 Shut off the extender
2 Log into the router and reserve a block of address for static IPs. In my case 192.168.1.2 - .50. Anything on the network will then be bumped to 192.168.1.51+
3. If a device can operate on both 2.4 and 5G, chose one and forget the other or you will have to repeat steps
4. Assign static IP addresses for each device.
5 If you really want or need to have both 2.4 and 5G on a device you will have to add another static IP for the other network as The Pit pointed out, MAC randomization creates a new MAC address for each network a devices connects to (one for 2.4 and another for 5G)
6. Reboot the modem, turn on the extender
To keep things simple, we kept all devices on 2.4, allowing the extender to sit alone on the 5G network.
Everything works perfectly now, both on the Netgear app, and ESET's Connected Home Monitor.
Thanks again