Most PDFs not syncing on iPad

I have checked many other questions regarding troubles syncing PDFs onto iPads, but none of the solutions have worked for me. I just recently downloaded Mendeley on my laptop and iPad (both iOS) and directly dragged files onto Mendeley desktop. I then logged in on my iPad, and though the information shows, only about 7 off the 100 or so PDF files I uploaded are viewable on my iPad. I re-downloaded, logged out on all devices, and tried re-uploading files, but nothing has worked so far and I am still unable to view most of my PDFs on my iPad. Thank you in advance for your assistance.