Every image upload the library refuses now writes an image_upload.rejected log line with the reason (too_large, empty, unsupported_type, heic_conversion_failed, upload_failed, not_staged, not_saved or storage_full), the file's extension and size, and the type its bytes were read as. The file name is not logged. Before, the log recorded only how many files were refused.
Refused image uploads are logged with their reason
Each image the library refuses is logged with why, so a refused upload can be explained afterwards.