
MS has a desktop tool you can download from your O365 account under tools - however if you are running Office 2013 it will report that you don't need to run it.

Try removing those and see if the issue persists - if it goes away, try re-adding them one at a time It may be they just needed to be re-added after some action occurred, or it maybe permissions have changed on one of those items.

Other things to look for are if you are connecting to other calendars (Exchange or SharePoint). To Manually configure your connection you search for that phrase directly and you'll get good results. I recommend manually configuring your client and notify your Admins (if you are the admin - review all your DNS settings). If you are showing legacy connections (anything not O365) your organization may have issues with how they have configured Auto Discover. Verify all your connections are pointing to O365 and not a previous/legacy Exchange server (look at server names - they should all be ). In your task bar notification area find the outlook icon CTRL+Right Click and select "Connection Status".

Under Calendars, click Sync calendars from, and then click Outlook.

The file you select will appear in the File Name text box. The Open Outlook Data File dialog box will appear. Click on the Open Outlook Data File button. To Find and view an archived item, click on the File tab from the menu and select Open & Export on the left pane.The Archived Folders will not appear until you have successfully archived your old messages for the first time. To add the shared mailbox to Outlook on the web, complete the following steps: Sign in to your Microsoft 365 account, and then select the Outlook app.
