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#11
One thing that does come to mind, pinging a lot of devices will result in a 100% packet loss, this is by design for security purposes so many of the available IPv4 addresses will appear to be unused even when they are actually in use
Most routers will have an option to "not respond to ping on WAN interface" or similar, this option will cause the ping request from the external device not to be answered this giving the impression that there is no device connected. the reasoning behind this facility is that a lot of malicious hackers will ping multiple IP ranges and then concentrate on those that reply showing that there is a device connected