I use ZipRenditionsManagement Component to add attachments functionality in content server, it was working fine but someday a customer reported a bug for me that attachments is not working. I don't like this kind of bugs, I searched for a solution to that bug but failed.
While I am tracing, I queried 'Revisions' table and I found the bug, tow document one takes attachment and the other one doesn't take, the difference between them was in the value of the field 'Rendition1' one took 'z' and the other took 't'. 't' means thumbnail and 'z' means zip renditions which means thumbnails and zip renditions can not work with each other. To turn off thumbnail, turn it off from inbound refinery.