Started experiencing the same error out of the blue yesterday in Outlook VBA. Finally found a workaround.
Changed this:
Set teamBox = objNS.CreateRecipient("Our.Shared.Mailbox@domain.tld")
Set olTeamBoxItems = objNS.GetSharedDefaultFolder(teamBox, olFolderInbox).Items
To this:
Set olTeamBoxItems = objNS.Folders("Our Shared Mailbox").Folders("Inbox").Items