@TeamYouTube I have tried everything to upload a custom thumbnail, and every single time it says: “Failed JSON input” I have tried clearing browser cookies and history, turning off extensions, but nothing works.
But when I use another browser besides Chrome, It does!
Noted. To help the right team better investigate, can you send a feedback report from the device and account having the issue? Steps here: https://goo.gl/WdI0BK . You may not receive an individual response but the details will help us identify and fix any issues, thanks.