Problems with the website used to store streaming video

I have a server to store video data and at the same time there are almost at least 500 people playing their videos simultaneously with different videos

But I'm having a problem where if too many users are playing the video will lag,

Low CPU and RAM usage as shown in the screenshot,
Upstream traffic always reaches 80mb, and if it reaches 80mb it starts to lag, if it's below that it's safe.