Thanks for reaching out. To clarify, you can update the custom thumbnail at the end of the video processing stage in the upload interface. Let us know if it still doesn't works.
@TeamYouTube This has been happening for over a week now whenever I try to upload a custom thumbnail while a video is processing. Is this going to be fixed soon?pic.twitter.com/9nkA3RRu75
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Thanks. Twitter will use this to make your timeline better. UndoUndo
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