Hello, i have a similar issue with my new PC that i managed to resolve by going to my task manager after the game has started, go to the details tab and set the ' affinity' for supreme commander to only the first 4 cores of my cpu. This completely solves it for me, even though i do need to do it every new game.
I got he info from this steam forum thread: https://steamcommunity.com/app/9420/discussions/0/601895119916956285/?l=latam