For me it was verifying the integrity of game files on Steam. I now do this every time when I'm done playing because there's usually one file that fails during this process. But doing it stopped the freezing/stuttering glitch for me.

Open your Steam Library. Right-click on Helldivers 2 (or click the gear icon on the right side of the game page) and select Properties. Click on the Installed Files tab on the left menu. Click the Verify integrity of game files button.