Massive FPS Drop & constant crashes

I am playing ark and the DEVS didn’t answer so hope you can help.
One Thing is that my FPS is dropping from 55 to25 FPS when ingame the day passes and the night begun. I use all EPIC graphic Options. I think 100% it is the fault of your programming of the shadows because when shadows are on High there is only a drop of 10 FPS.

The other Problem is that after a period of a Special time the game crashes with the folloowing Crash dump stacks.

My Spec

i7 2600k 4.2 GHZ
GTX 1080 2 GHZ overclocked but no other game crashes
16 GB DDR3
Game UE Version : 4.5.1