[Outlook 2011] Some emails don’t download attachments, They just sit there grey.

I have many clients of mine who are on the most updated version of outlook 2011 that are having their attachments just sit grey and never download. It is not all of their emails just some of them. You can forward the attachments because they do not appear in the email and clearing the cache didnt fix the issue either. These are office 365  exchange accounts. Right now as a workaround I have them going to the web portal to download their attachments. Any advise would be much appreciated.