After restarting the computer, the rendering speed increases fourfold!

After restarting the computer, the rendering speed increases fourfold! How can I make this work without having to restart? To clarify: only one program is running—either Premiere or Encoder. The hardware performance remains the same. What could speed up the rendering so much? 2 hours versus 30 minutes—that's a huge difference! Once again—I turn on the computer, run the render twice (which takes 4 hours). I restart the PC and the render finishes in 30 minutes! Technically, this would be impossible if the problem were hardware overheating.