Even though we add the autoplay parameter to the video URL automatically with WP Video Popup & WP Video Popup PRO, most browsers nowadays tend to ignore it.
A lot of browsers have changed their autoplay policy and won’t play videos automatically even with the URL parameter assigned.
One workaround would be to mute the video by adding the mute="1" parameter to the shortcode. It’s still not guaranteed that this will work for all browsers.
Unfortunately, there’s nothing we can do on our end to avoid this at this point in time.