I get this error when I do a Bulk Smush

Error posting to API: 500 Internal Server ErrorError posting to API: 500 Internal Server ErrorInvalid file format. Only PNG, JPEG, and GIF files are supported.Invalid file format. Only PNG, JPEG, and GIF files are supported.Error posting to API: 500 Internal Server ErrorError posting to API: 500 Internal Server Error

I am assuming there is some corrupt files. How can I view the log or debug this?