Searching Public Folders & Shared Mailboxes - Office 365

[Joel]

Does anyone know how to get the search function working on Shared Mailboxes and Public Folders in Office 365?

We're using Outlook 2016.
One user (User A) has 2 shared mailboxes (User B, User C) as well as Public Folders.
When User A wants to search for mail within User B's or C's mailbox, no search results come up - only data from UserA's mailbox appears....even when selecting 'Current Folder' after selecting UserB/C's mailbox.

This is the same behaviour with the Public folders. It seems Office 365 doesnt let you search for content within shared mailboxes or public folders.

I have tried the steps in here - https://support.microsoft.com/en-gb/help/3169741/no-search-results-or-content-displayed-in-public-folder-favorites-in-o but no luck!

Has anyone been able to successfully search these additional folders?