Question / Help Videos are unstable at the beginning

[Syltom]

My videos are slow and unstable at the beginning, but it runs normally and smoothly later (around 4:50 mark and later). Also, everything runs smoothly when I play the game, it's just the problem with my recorded videos.

Could someone please help me, what the reason of this problem is, and how I can make my videos stable from the start? Thank you very much.

Here are the OBS settings that I am using:

And the information of my computer: