Group Calendar Stopped Showing in Outlook App

I have the same issue with at least 3 users/machines (including mine). I can see the Group Calendars via the web and Mac Outlook, just not within the work PC Outlook.

First > I performed an update of Microsoft Office within Outlook (File > Office Account > Update Options). This *initially* worked for me after the update, then reboot of the PC. However, when I closed Outlook and reopened it, the Group Calendars were again no longer visible. I tried this on the other PCs and it did not work at all.

This is what I most recently did:
Some did not like the apps showing on the top, left (where they were moved with an update) and preferred them to remain at the bottom. So, I had made the setting change to allow that. When I undo that change, the Group Calendars now show (even when I close and reopen Outlook). However, this seems to have worked for one, but only temporarily for another.

Steps: File > Options > Advanced > (return Check to) Show apps in Outlook

Seems like making this change (adding or removing the check) momentarily "fixes" the issue for some, while only temporarily (if Outlook is not closed and reopened) for others.

** UPDATE** This seems to be holding....

I ran a fix from this:

(2018) Group calendars show in Outlook 365 but not in desktop Outlook 

• Close Outlook.
• Right-click on the Start button choose, Run and type this in the open field:
  outlook.exe /resetnavpane
• Close Outlook.
• Restart Computer.

Now seems to be back to displaying Group Calendars even if I close/reopen Outlook.