It's kinda strange because I've had this problem before. I'll close down the game completely and my RAM still shows like 90% or something. I obviously go to the task manager and there is nothing there. The only thing that seems to fix it is a reboot. My computer even after closing the game still actually thinks it's using the RAM. I have 8GBs so this shouldn't be happening. I've already checked my RAM and it's still good.