How to Fix / Restore Access to Shared Calendars in "the new Outlook" 2019

At the University of Pennsylvania, our Office365 users suddenly lost "edit" access to the shared calendars they had previously set up in their O365 calendars. The calendars still appeared, they just weren't modifiable. This is a huge deal, because we schedule many public spaces and manage staff schedules through shared calendars.

The cause?

The issue seems to be tied directly to "The new Outlook" option being enabled in the online version of O365 (http://outlook.office365.com). Users who are NOT using "the new outlook" are not affected. Apple Calendar users, who have their O365 calendars set up, also do not seem to experience issues. Very strange.

I took a look at the shared calendar account these folks were trying to access (which did have "the new outlook" enabled and most of the user permissions had been partially wiped!

What the heck!

The fix?

Note: Make sure "the new outlook" is enabled in both O365 wemail AND calendar.

I found that re-adding a user's permissions to the source calendar (visit the source calendar that is being shared -> right click on the calendar name -> "Sharing and permissions") will trigger an email to the user about their "new" permissions to the shared calendar. If they click the "Accept" link in the email notification they receive (from within the ONLINE version of Outlook at http://outlook.office365.com), followed by a browser refresh, they're back in business.

Also, switching "the new outlook" back off does not seem to cause any issues.

But that's not the only change:

• For the user accessing the shared calendar account, the calendar now appears under the "People's Calendars" section rather than the "Other calendars" section.
• Shared calendars now appear in the listing of O365 calendars accessible on iOS devices (this is great)
• A user accessing a shared calendar can rename the calendar to whatever they want (for their view only). And if they rename it via Outlook.office365.com, the name syncs to iOS (but not the other way around)