The Outlook desktop application does not support more than 1 shared mailbox.
Therefore if you have access to more than one shared mailbox within your Outlook and encounter problems with it not updating etc, then please switch to using the online/browser version of Outlook.
Open a browser and sign in to office.com with your Domino credentials
Clicking on the Outlook icon as above, will take you here:
Next, click on your photo or initials in the top right-hand corner of the browser window and select Open Another Mailbox
A dialog box appears in the middle of the screen with a box. Type in the name of shared mailbox you wish to access or search the directory
Click Open
The shared mailbox should open in a new browser tab.