Outlook Web App Attachments in Office 365

hi there, we have a very strange thing happening in the Outlook Web App in Office 365... When attaching documents from OneDrive it just spins and doesnt attach. Thing is, that it doesnt happen all the time and seems very intermittent.

Has anyone had this issue recently ? More wondering if Microsoft have changed something which Fortinet hasnt caught up with yet (as in a new IP or something)

Thanks