Sometimes the upload process on the server changes from assembling stage to publish stage even though the last byte of a file has been upload but not become part of the assembled file (last byte of the file is missing). The file never the less gets published, but no thumbs are generated because of a truncated PNG IEND chunk.

Web browsers, MS Windows, Exiftool and GIMP do display PNGs with a truncated IEND chunk, Mastodon rejects such files.

Examples:
[[File:Diversity_2023_25_(video_capture_049).png]]
[[File:Diversity_2023_25_(video_capture_194).png]]
[[File:Diversity_2023_25_(video_capture_268).png]]
[[File:Diversity_2023_25_(video_capture_529).png]]

What should have happened instead?:

Either these files should not be accepted for publishing at all, or thumbor should create thumbs never the less.