This issue usually happens when I am playing multiplayer game rather then singleplayer. My frames ar much lower in Multiplayer game and they fluctuate between 20-30. Although game is pretty stable in havely populated base or in battlefield.
Although it is sometime happenes that while multiplayer gameplay my frames drop drastically, and it cause freezing of a game for couple of secounds. Sometime games will start working proparly again, or it will result in crash of the game or displaying of the message Arma 3 stopped working. I even posted the bideo on YouTube that shows the performance of the game https://www.youtube.com/watch?v=psq9TE6LSuI . So as you can see the game works pretty decent on my PC ommiting this suddany freezes. I turned off my anty-virus program or other programs that could affect Arma performance.