I can confirm you there seems to be some issues with the implementation we currently use for our Internet check launch condition. Currently we use the INetworkListManager::get_IsConnectedToInternet method from INetworkListManager interface
and it seems this solution does not offer foolproof Internet detections all the time.
We will try to analyze and implement a better solution in the future and hopefully this improvement will be available in one of the next versions of Advanced Installer. When so, we will update you on this forum thread too.
All the best,