User's personal CALENDAR appearing as generic SHARED CALENDAR

[SW-SoCo2]

We have a user whose personal CALENDAR is showing up under SHARED CALENDARS (both Outlook desktop app and office.com Outlook web app) --- it seems to have lost some sort of attribute(s) that identifies it as the Outlook user's own CALENDAR and/or has grabbed an attribute that makes Outlook think it's a SHARED CALENDAR:

Typically, users will always see their own CALENDAR directly under MY CALENDARS, with their UPN/email included as an identifier:

The calendar itself seems functional and user is able to add/change/remove entries.

All sharing permissions/delegates have been removed - to no avail.

Has anyone seen this before? Any suggestions on where to look? TIA.

[#2]

@SW-SoCo2 I have a user with the same issue. Did you find a fix?

[#3]

Unfortunately not. I finally opened a support ticket with Microsoft, and spent some time with the support engineer mining through various settings using MFCMAPI --- to no avail; so I finally gave up. In this case, it's a mailbox profile that's been moved/migrated many times over the years, including from an older on-prem version of Exchange. I'm eventually going to just back up & then export the mailbox to PST; delete the existing mailbox; create a shiny new mailbox for the user - and then selectively import the needed email & calendar data.

[#4]

@SW-SoCo2 I had a user experience this as well. Calendar permissions have select staff with edit rights, but all internal. 

In OWA, user's calendar appears in category "People's Calendars."