We've taken a look at the video and see that the thumbnail is working fine. Could you try clearing the cache and cookies of your browser and see if it helps? Here's how: https://goo.gl/dwzcyo . Also try using a different device/browser. Keep us posted.
@TeamYouTube @YouTube @YTCreators my video has been up for 2h and my thumbnail will not loadpic.twitter.com/s9pgLxAaTE
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It took around 3 hours when it loaded
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