Outlook 365 Classic - Contacts problems

Outlook version 2506 (Build 18925.20168 Click-to-run)

I've using Outlook (part of MS Office for more years than I care to remember and have despite its quirks been quite comfortable with it.

A couple of years ago I moved to Office 365, now Microsoft 365, and continue to use Outlook (Classic?) and other members of the suite.

A few weeks ago I got a new PC running Windows 2011. Installed MS 365 and brought my .pst files across from my old Win 10 system. All ok. Or so I thought. I could send emails, autofill addresses, do all I needed with calendar, notes, etc.

I then went to edit a contact, clicked on the Contacts/People app to the left of the navigation bar, amidst the Mail, Calendar, People, and More Apps area to find all my contacts were missing. After much puzzlement and hair tearing I went to create a new folder and suddenly all my contacts in their various folders appeared. Great I thought, I could add a contact etc.

Then earlier today I needed to add to one of my Distribution Lists - aka Contact Group. Opened the group, clicked Add Members, then tried both From Outlook Contacts and From Address Book found empty contact lists. Clearly the contacts are there but not being recognised for me to use in this way.

I then added the new contact using New E-mail Contact and manually added the details so my immediate problem was solved. Clearly this new contact is being stored somewhere differently as when I try again to add to a Contact Group either by Outlook Contacts or Address Book it offers me the contact I'd added manually.

Clearly Contacts are being stored in a different place or a different way.

So what's changed and/or have I done wrongly.

Not sure, but it sounds like Outlook does not have the Contacts Folder you brought over from your old PC as a member of the Address Book?

Enabling the Contacts Folder as an Address Book | Slipstick Systems

Reads like you’re experiencing a conflict between contacts stored in PST files and what Outlook recognises in its Address Book or for Contact Groups. This could be because Outlook is using a PST file as the primary store in a Microsoft 365 setup.
So the contact folders aren't properly set to be included in the Outlook Address Book.

Im not using Microsoft 365, but you could try the following…

• Open Outlook.
• Click the People icon (bottom-left or side-left pane or wherever you found it).
• Right-click the contact folder (the one where your contacts reappeared).
• Choose Properties.
• Go to the Outlook Address Book tab.
• Tick the box: Show this folder as an email Address Book
• Click OK.

And so you know, contacts can be selected, like emails (Ctrl + A = Select All) and copied/pasted into another folder, like another contacts folder (Ctrl + C = Copy / Ctrl + P = Paste) OR just drag them to the new folder. But copy/paste is safer so you have the originals for the time being. You could also select all and hole the Ctrl key fown as you drag the addresses over. Holding the Ctrl key makes a copy, holding rubbish key moves.

Create a copy/backup of your PST file first.