Your GPU cannot keep up with OBS and playing SCUM at the same time, even on the lowest settings at 1080p. Best you can do is going to the config file and limit your FPS to 30.
In order to do that method it's found in C:\Users\Username\AppData\Local\SCUM\Saved\Config\WindowsNoEditor and the option is under GameUserSettings.ini on the line FrameRateLimit. If it's not there, create it under the section [/Script/Engine.GameUserSettings].