There's a few websites I've been to where this methodology doesn't work, and it's not because there's no m3u file or whatever. Some sites will work fine but then the moment I open dev tools the site will freeze. I think the site knows when I open dev tools and makes itself essentially crash.
They mostly use inline JavaScript to determine if the dev tools are open. If open, then they put you in a loop that will only end of the tools are closed. Normally when this happens the debugger will "pause" at the line in question.
If you know how to use the "unlock origin" extension, you can then block the JavaScript inline function so it won't run. Then the page will not stop when the dev tools are open.
You can Google how to block inline JavaScript with ublock origin.
The ublcok solution above works fine, but you don't have to use the dev tools while in the site. Just F12 before going to the site -> performance -> start recording -> close dev tools -> visit site and start watching the video -> close tab and back to dev tools -> capture recording
edit: this way you are capturing all network traffic without dev tooll