New Outlook - Imported csv Contacts 'half' Showing

Are you using the new Outlook app or classic Outlook on a new computer? 

If classic Outlook - that usually means the addresses need to be resolved.  Try this: open one contact and click in the address field. Press Ctrl+K or click the resolve button on the ribbon. Save and close the contact. 

Now click the To button - do you see the address? If yes, the addresses need to be resolved. If you have a lot, I have a macro that can do it - Imported Addresses are Missing from Address Book 

(I'll convert that to a PowerShell version but won't be able to do it today.)