The video takes a few seconds to load
YouTube has recently decided to display a lot of information and options for a few seconds when the video loads for the first time.
To avoid displaying that information in your store, we keep the video thumbnail during that time. So, for a couple of seconds, your video will only display an static image, like in the following screenshot:
If we did not show the static image, something like to following would be displayed in your store:
We consider that this is the best option for the current YouTube behaviour. We will monitor YouTube changes and, if the situation changes in the future, we will adapt our app to take advantage of the changes.