Uh, yes. Many times.

How countries attempt to block Signal Private Messenger App around the world

This report shares OONI measurements on the blocking of the Signal Private Messenger app in Iran, China, Cuba, and Uzbekistan.

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The Verge

Signal has been blocked by Venezuela and Russia

Signal is aware of the blocks.

The US gov. has access to signal. Through the US gov all friendly states have access to data in signal. That is why the CEO of signal is not put under arrest and anti US gov try to block signal