Low fps the first 5-10 minutes after starting the game

When I start the game the fps gets lower than normal for like 5-10 minutes and then it goes back to normal after that, as you can see in the attached video. The normal fps is +250 and when the problem happens it gets below 60 and sometimes hits 20 and only happens in Overwatch.

things that I've tried:
reinstalling the game
updating windows
DDU

PC SPECS:
i5 9600k
rx 6700xt

16GB RAM

any idea how to fix that?

(in the video I changed the framerate cap but that didn't fix the issue It got fixed by itself, because I tried that before and it didn't fix it)

https://reddit.com/link/1cabnwg/video/eqm7wmuqe1wc1/player