Graphics issue randomly in world

Not really sure the circumstances surrounding this, however the graphics jump between normal and what is shown in the screenshot for about 3 seconds or so at random intervals while playing. Note that my FPS has dropped from 300+ to 7 while this is occurring. This is quite an intermittent issue happening maybe 3-5 times within a 2 hour session of playing. Also using recommended graphics drivers so im unsure as to the cause, it's also only the actual game world that glitches out. The main HUD appears to stay