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Whenever I try and upload a new thumbnail it will show the new one in the menu, but the save button will just say "loading" indefinitely. I have this problem on a few videos now. One I uploaded before the website change and it worked for a while, the update seemed to break the thumbnail and I can't fix it, the second I tried to upload today and can't change it.
I've tried both jpegs and png's, and I am using chrome.