I'm experiencing an issue with Buffer where images initially upload fine, but after 2-3 days, some of them show errors

I’m uploading PNG files to a Notion database and then retrieving the file URLs, which are hosted on Amazon S3. Since the URLs are generated and uploaded to Buffer at the same time, I don’t think this is an expiration issue. If it were an expiration issue, I would expect the images to fail in sequence, but that doesn’t seem to be the case.

How can I troubleshoot and resolve this problem?