TikTok's in-app browser not loading html/css code for videos

Question

I currently have this html code:

<video playsinline="playsinline" autoplay loop="" preload="auto" muted poster="" class="fullscreen-bg__video">
        <source src="my video url" type="video/mp4">
</video>

This code works perfectly on every browser including for mobile. It even works for in Instagram's own in-app web browser when you tap on a link/open something in their app. However this doesn't work for TikTok's own in-app web browser. Didn't find much resources on this especially debugging in-app web browsers so any help is much appreciated!

Don't think this is needed but here is my css code as well:

.fullscreen-bg__video{
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    z-index: -100;

}
/* new div */
.cover {
  width: 70%;
  height: 100%;
}