Why my iphones randomly vibrates when watching live

Hello, am so confused about this. I was watching TikToks, scrolling on the app and when I saw someone is doing live from the creators of the videos i am watching I went to check them out but after like 15 second every time my phone vibrated super hard randomly and I don't know why this is happening. Is this some king of bug or feature? I don't get any notification at all. Thanks for any ideas.