Use a desktop or laptop as the sole device to accept/decline invitations.
#Outlook for office 365 dump sync cache windows
Additionally, Outlook for Windows and OWA have shown to be more reliable than Outlook for Mac. Assuming reliable coverage, you might, for example, be able to create new appointments on a device, but may not want to invite, accept, or decline meetings, or modify any recurring events, until you are using Outlook or OWA (or have successfully tested these functions on your device).