Apparently the game has an issue with multiple cores.
So go into the gamer profile of Ryzen master and disable Simulations multitasking (SMT) and enable Legacy Compatibility mode and then restart. This will most likely affect performance in other games, so enable creator mode again when you are done with the game...
https://steamcommunity.com/app/212410/discussions/0/
This solution worked for me at least, I had no luck with programs such as Runwithaffinity or Process Lasso