Low fps after start a match

I'm having a FPS issue with the game. When I open the game, everething is working perfectly, until I start a match, even at the offline, even at the menus, everething starts to lag, low fps and things like that. I saw on youtube that my graphic card (RX 580) and my CPU (R 5600x) are enought to play in 1080p on low with 60+ FPS.  But my game is lagging even at the menu!