Hi, as the title suggests. After an hour or sometimes two the games performance suddenly dropps really low.
I can get everything back to normal by restarting the game but since the loading times arent that short i got curious if anybody had the same issue and could provide some help.

Could be overheating on your processor or GPU. I'd get something like CPU-Z and/or NVidia Inspector to monitor your GPU/CPU temps. Also want to check your RAM capacity.

my graphic card goes up to 55° which should be fine and i got two DDR8 gb rigs.

Yep, WItcher is a beautiful game but if you want to run it smooth I would suggest investing in quality; high flow case fans. CPU doesn't like being overheated. Once mine hits 75 fahrenheit +/- 2 frame rate starts to skip.

The more you upgrade your hardware the better it looks.

it's not like i can't play the game at high settings or anything like that. the game just seems to pick a point at random, at which the game starts "stuttering" from time to time. not consistently.
well it's not that bad since it forces me to stop playing once in a while for a minute or two.

Try this:
Start, Documents, The Witcher 3.
Now Delete user settings, don't delete gamesaves.
Now when you start the game, go to options and set your graphic settings, etc.