The latest update of Signal introduces the domain fronting technique that has been implemented to circumvent censorship and restrictions applied by governments that want to avoid its use. Some states are already blocking the application with the support of ISPs. The Government of Egypt and the United Arab Emirates applied measures to block Signal, for this reason, the Open Whisper Systems who develop the app has revised the Android version introducing a technique called domain fronting. The technique relies on the use of different domain names at different application layers to evade censorship.”]
Source: https://securityaffairs.co/wordpress/54659/digital-id/signal-domain-fronting.html