Can't see all devices

I’m reasonably certain that GlassWire don’t say that they “monitor usage on multiple networks”. I can see why you might think that but the website info talks about what your computer or server has been doing on the network.

There have been a lot of requests for full network monitoring and the GlassWire team have said that they are looking at it, e.g.:

Many of us GlassWire users are waiting to see what they decide. The best option is probably to use a router protocol like NetFlow because it looks all packets. sFlow (sampled packets) is another option but not good if you want to see all traffic like GlassWire does. An older method like SNMP is also useful because it covers so much more than just the network. Packet-sniffing might also be a serious option although I’d be surprised if they choose it.