It might save yubico some support queries if the
AES upload form suggested that the keyboard layout could be at fault, whenever it detects a prefix mismatch. Took me a long time today to figure out that my dvorak keyboard layout was the reason the form kept giving me "OTP prefix mismatch" messages. I am sure I am
not the first to get bitten by this, too.
Even better would be if the upload form did the same checking for layout that the validation server apparently does, but obviously that would be a lot more work for someone.
Hope this helps.