When game have FPS lagg (i think when its loading new objects) if you open main menu, it increase FPS back to normal, but if you close it again, FPS drops back down.
Funny is, it can do this "fix" when standing on one place OR ALSO if you flying in helicopter or plane.
Screenshots are from multiplayer, but same problem is in singleplayer (tested with plane)
PS: I have FPS drops when leaving EVERY building on altis, even looking out of windows does lagg and game is instaled on SSD {F21984} {F21985} {F21986} {F21987}