Name Change Causing Calendar Issues

We have a user that changed their last name. We changed the login ID and UPN on-prem and made appropriate changes in Office 365. She receives her email and her own calendar items just fine in Outlook 2016 desktop.

She is the delegate for her boss and manages their calendar. What she finds now is that when she makes updates to the boss' calendar in Outlook 2016 the updates don't show up in Outlook 2016 but do show up when she looks in OWA.

We've redone the delegate permissions from the boss and in her Outlook 2016 Account Settings re-added the boss. 

We recently upgraded our users to Outlook 2016 from 2010 so a new profile was created for the user at that time.

We are at a loss at what is causing the calendar items from being seen in the desktop client but can in OWA.

Ideas?