Performance issues after time in Singleplayer

Hello,

I´m pretty new to Space Engeneers played first on Xbox and now on PC.

When I run the Game in Windowed (Fullscreen) I get CPU Spikes up to 400%. I figured out that when I play in normal Fullscreen. I dont get these spikes and the Game runs perfect in the first couple minutes. After a certain time I get the same problem and the Spikes are back. Even if I do nothing and just sit in the Pod in which I spawned on the planet. I´m sure that itshould have nothing to do with the complexity of the safe file as this occures already after loading into a fresh world and waiting for about 20 minutes the game starts to stutter. Has someone any idea which could affect this ? Maybe Virtualisation ? The game is freshly downloaded and has no faulty files. I also tried to turn down graphics but that did not help. I also disabled the shadows as I have read that this could cause some lags. As I mentioned earlier after about 20 minutes the simulation speed is going down from 1.0 - 1.02 to 0.8 without doing anything.

My specs are:

AMD Ryzen 5 3600X

AMD Radeon RX480 OC (8GB)

32 GB DDR4 RAM

Thanks for any help in advance.