When the gnirehtet app is used to reverse tether over USB, it simulates use of the VPN mechanism. Other apps on the phone have no network issue, such as browsers. But SIPdroid 4.4 beta fails to detect the network. In the profile for a SIP account there is an option to connect over VPN. After enabling that it still fails to connect.
FWIW, the LinPhone project had the same problem 5 years ago:
When the gnirehtet app is used to reverse tether over USB, it simulates use of the VPN mechanism. Other apps on the phone have no network issue, such as browsers. But SIPdroid 4.4 beta fails to detect the network. In the profile for a SIP account there is an option to connect over VPN. After enabling that it still fails to connect.
FWIW, the LinPhone project had the same problem 5 years ago:
https://github.com/BelledonneCommunications/linphone-android/issues/709