I've been having this issue ever since I got my R7. At random moments, beginning at around 10 minutes after I start a game, I will get insane FPS lag, and input lag. My FPS will drop down below 10, and if I attempt to move the mouse, it will move on my screen a second or two after. This will last for approximately 10-15 seconds, then completely go away for the rest of my gaming session. I've experienced it in Battlefield 1, OverWatch, and H1Z1 mainly, but it has occurred in a few other games as well.
Asus Prime B350-Plus
Ryzen R7 1700 @ 3.8GHz
16GB (8x2) Corsair Vengeance DDR4 RAM @ 2666MHz
Sapphire Nitro R9 390 (Stock Speeds) 8gb DDR5