I am experiencing the same issue as OP.
Game runs around 50 - 60 fps for 30 minutes.
After 30 minutes frame rate SUDDENLY drops to ~ 4 fps and STAYS there until game has been restarted.
This is only present on DEV-branch (16/04/2016).
My friends do not experience this problem when we play together.
Experimented with graphics settings, no effect.
Specs:
Core i7 2600k @ 3.8GHz
GTX 680
Windows 7
250GB Samsung EVO SSD
Other Info:
The frame rate drops from ~50 Hz down to ~4 Hz over a period of 13 seconds. However, when frame rate drop occurs, looking up and down appears to speed up the rate at which the frame rate is dropping. (from 13 seconds down to about 5 seconds)
I hope this was helpful.
