when you first logged into the server, when you click on the right mouse button to look through the scope, the weapon fires! However, the second (additional) mouse button is set to aim only. This happens only when you have just entered the server. I play on the official European server (without mods) ‘3842 | EUROPE - DE | 1st Person only’. (PC version)
Imagine this situation: you approached a military base and finished the game. You decide that tomorrow you're going to go check it out. Next day: You just appear on the server and decide to look through the scope with optics to see if there is anyone. Instead of that, you have a loud weapon fire, which notifies everyone that you're there.
It's just maximum stupidity