[HELP] Hard stutter after first game

[Stoxxed 0]

Hello guys, I have a problem, when I first launch the game it runs pretty smooth (40 to 60fps) on most maps (except for reserve wich is choppy but still playable. But as soon as I launch a second game (whatever the map is) I have a massive dop in perfs : loading the map takes ages, and when in game I'm between 1 to 20 fp depending on map. If reboot the game everything works fine again, until I play the 2nd game...

I tried a lot of things : changing the pagefile size, setting the windows clean memory task, tweaking in game and radeon settings, re-installed the game 5 times on different drives (currently on a SSD), activating "Clean ram auto" and "Only use physical cores", using a batch to launch EFT in high priority... kinda out of ideas here.

EDIT : also, I have no over-heating issue, I applied new thermal paste to both my GPU and CPUl, they go up to 70° max on full charge.

EDIT 2 :

System Specs:

Interl I5 6500 3.2Ghz

Radeon RX 570 8gb

8192 mo

SSD 1 TERA

Playing in 1080p

Anyone can help me ?