Reproducible on chell:

network_WiFi_DisconnectReason.disable_client_wifi is not actually collecting any disconnect codes. This was previously not visible, as network_WiFi_DisconnectReason did not ensure that the disconnect codes collected from net.log were actually generated by the current test until this CL:
    https://chromium-review.googlesource.com/c/chromiumos/third_party/autotest/+/1128210

Based on the log files, it does look like wpa_supplicant has a CTRL-EVENT-DISCONNECTED with a -3 disconnect reason (as expected). However, shill does not log a supplicant disconnect event, which is what the current network_WiFi_DisconnectReason implementation looks for.

In particular, when the wifi interface is disabled through dbus, shill doesn't log a disconnect (due to Wifi::Stop() being called before getting a disconnect message from wpa_supplicant?)