downloading multiple files does not work for more than one file

I use the download field of multiple files in my content type "X" with a custom ajax field. But my multiple file download does not work at all, only one file is downloaded at a time. I thought it was because of the ajax field, so I deleted these fields, but it also does not work in the content type "X". Although this field of downloading multiple files works perfectly in the content type "Y". I do not know where is the problem?