Mac OS and iOS users who use Safari (v 9) are unable to view calendar entries using OWA.
[Oct. 22, 2015] Apple computer users who use Safari v 9 are unable to view calendar entries in OWA (Outlook Web App). Microsoft/Apple are aware of this issue, but there is no word yet on when/if a patch will be available to correct this. This issue also affects Safari users on mobile devices who are running iOS v 9.
Users who wish to view calendar entries using OWA can use an alternative web browser. Current versions of Firefox and Google Chrome both work with OWA's calendar without issues.