Entering ADS with a semi-auto weapon immediately after you fire a shot makes you fire again regardless of whether you hit your fire key or not. You can even spam your clip empty by timing the ADS toggling right.
After doing the ADS firing enough times it “fixed” itself but instead quickly tapping the ADS key played the firing animation without actually firing the gun (the second clip in the video). It also muted the sound effects from the main menu afterwards.
Seems to happen with every semi-auto weapon except the sniper rifle.
In these clips I’m only hitting the fire key for the first shot to start the sequence.