Question / Help Encoding Overloaded, yet no causes I can see

I just found a VERY reliable way to create the problem, but have no clue how to fix it!

When I click into OBS, the framerate of the game (GTA V) drops to ~15 and stays so until I click on another window. The encoding becomes overloaded until I restart OBS, and streams completely fine unless I click the OBS window.
 
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