Download zip file not functioning correctly

per my clients (not good) …… either only 1 or 2 photos make it into the download zip file, usually the first 1 or 2 photos, or all the photos selected make it except one random photo. Clients assure me they are selecting them correctly. when I checked the 1 random photo that didn’t load… it was selected in my browser — super weird.

does a relationship exist between what I may select or unselect during wordpress pixproof file creation and what clients experience?

is there a fix for this?

Most clients select and download there photos with no issues.. why are only a handful of clients having these issues…. ?