Hi Laurence,

There is a size limit that is controlled in the global.xml for uploading attachments in the profile Globals section:

Please check the size of the zip file versus the limitation defined in the global.xml.  Seeing as these are already registered as links, I think you are probably ok but just confirming.

Also can you try right-click on the link instead of left-click.  See if you have a Save As option for the file.  In my Edge browser for the Web Employee Portal, it downloads the file automatically to the Downloads folder.  Perhaps you are missing the notification if using the web browser? Check the downloads folder. In the Astea Browser, it opens the IE dialog asking if you want to open, save or cancel.

I have seen strange behaviour in the past when the files are removed from the server by an external process outside of Alliance.  This leave the database record in place indicating there is an attachment but there is no file to download. You may want to see if the physical file still exists or not as well as compare the file size with this setting. 

Last thought I have is perhaps you have security software that does not allow you to download zip files from a website.