I'm not good at English, so I use google translate. Please use English or Japanese:
From a few days ago, the thumbnail images disappeared from the two videos I posted. So I tried to re-upload the video from "Edit" of the video and fix the problem, but when I finished and "Save" I got this message:
「The content on this page has either been modified by another user, or you have already submitted modifications using this form. As a result, your changes cannot be saved.」
Can anyone please tell me why this message was displayed and how it can be resolved.