@TeamYouTube why has my video thumbnail suddenly dissapeared? I don’t have the thumbnail anymore to re-apply it. Its on my old computer. #HelpPleasepic.twitter.com/5CP5jwTTE4
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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.