It is possible to change networks in a way that can't be detected by differencing IP addresses; the user could switch between two WLANs where they are assigned the same IP address on the private subnet. Paul Jensen suggested looking for WLAN SSID changes to mitigate this potential problem.

https://chromium-review.googlesource.com/c/chromium/src/+/1066074/13/net/base/network_change_notifier_fuchsia.cc

The implementation is blocked until Fuchsia adds WLAN support and exposes SSID information through the netstack FIDL interface.