We have added some new enhancements to Exchange and Office365 support, including calendar and contact sync. For this to work well, can you please remove and re-add that account.
For these to work well, you may need to remove and re-add your account as ActiveSync.
To remove your account, please tap More (o o o) | Various Account Settings | Select the account you would like to remove | Edit Account and then Remove Account.
When re-adding the account please select Add Other Account | Exchange | ensure the ActiveSync checkbox is enabled and continue to add your account.