Run OBS as Administrator. By running your game un-capped, it is using up all the GPU processing time, and OBS needs a very small amount for its internal housekeeping tasks (scaling, color conversion, compositing, etc). By running OBS as Admin, OBS can claim GPU priority and handle its tasks before the game eats the rest.
The other workaround is to run a framerate limiter on your game, such as vsync, to ensure it does not use all the GPU time and there is still some left afterward for OBS.
Also, DO NOT run OBS in Full colorspace mode. Use Partial unless you are only recording, and have an end-to-end Full range production pipeline in place. OBS is hardcoded to only stream in Partial, and having Full selected will result in significant color crush and a washed-out appearance.
