Summary:

When pressing the screenshot regardless of graphics settings, it will lower the frames per second and gradually keep lowering it. It does stop at a certain point. Only way to get higher fps was to change my graphics between fancy/fast. Ex: was at 140 fps in nether then it dropped to 40 and stayed between 40-60. 

Steps:

Have debug open. Press screenshot button. And to fix it, change between fancy/fast graphics.