I'm also experiencing some unusual behavior in my Lambda function. I've included a mime.types file to help detect the correct MIME types, but for certain files, the MIME type is being detected incorrectly. For example, a PPT file is being recognized as a application/msword hence DOC file was detected. This issue doesn't occur locally; everything works correctly with the same configuration(python version, library version except the os). Does anyone have idea why this thing is happenning?