iPhone Black Display Screen Using Video Tag

I build websites and my current build has seven videos on the first page built with the html 'video' tag. The page renders on all browsers and Android and on Safari on my mac but on my iPhone safari they appear black and then play correctly when clicked. This has changed since the last update.

It would be helpful to have a look at the code. Though is it possible that the video’s don’t have a poster image?

<video poster="example.img">
</video>
iPhone Black Display Screen Using Video Tag
 
 
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