If you are on about when the game drops to 3/4 FPS and looks like something made in the stone age, I know a temporary fox for it, it usually used to work for me and eventually the FPS bug stopped.
It is a weird fix, but worked for me.
1: Tab out of game
2: Open task manager
3: Tab back in to game
That is literally it, if it works for you, it will work for around 2/3 minutes. So in that time, if not in combat, sync your data and log off, or hide somewhere safe. You will need to fully close down Arma 3 and launch it again to sort the issue out fully though.
If it is not the 3/4 FPS bug, I have no idea.