Once the free memory is exhausted, performance takes a big hit - games with heavy caching like BF1 suffer horribly. The only way to fix it previously was restarting the computer (thus clearing the memory), which explains why it was only happening after a while and not on a fresh boot.
Use this instruction and choose executable. Don't turn off CFG globally - it's a major security breach.
Two Frame Buffer Reverting In Game Workaround (dx12 only)
The video setting of Future Frame Rendering can be set to "on" or "off". Depending on hardware configuration one could see an decrease or increase of performance and may notice a corresponding shift of less and more input lag. For a full explanation of what this setting is and how it functions see here.
When running the game in dx11 and attempting to set the frame buffer to 2 (IE RenderDevice.RenderAheadLimit 2), either via console command or user.cfg file, the game will quickly revert back to a 1 or 3 frame buffer upon death and re-spawn of the player depending on if one has future frame buffering set to off or on correspondingly.
To fix this:
The game should now consistently use a two frame buffer and not revert to a 1 or 3 frame buffer upon player death or map rotation. To test what the current frame buffer is at any time simply open the console in game and type "RenderDevice.RenderAheadLimit" without the quotation marks and hit enter. A value of 2 should be returned upon following these instructions. This workaround currently only works in dx12.