iCloud Contacts suddenly wrong on my Mac; right everywhere else

Hi PeterORiordan, We appreciate you reaching out to us. We’d like to gather additional details that may help us be in a better position to assist you.

1. Did you remove any mail accounts that may have been syncing contacts as well?
2. Also, do you have a different Apple device that is signed in to the same Apple ID? If yes, are you experiencing a similar issue with your other device?

These details can help us in isolating the issue.

Let's check if the issue persists while on safe mode.

Safe mode does a basic check of your startup disk, similar to using First Aid in Disk Utility.

Performing this step may help resolve the issue, or further isolate the issue.

Below is an article to help guide you through the process.

How to use safe mode on your Mac

If you are experiencing the issue on safe mode, let’s test if the issue persists on a newly created user account. 

Performing this step will help in isolating the issue.

1. On your Mac, choose Apple menu > System Settings, then click Users & Groups  in the sidebar. (You may need to scroll down.)
2. Click the Add Account button below the list of users on the right (you may be asked to enter your password.)
3. Click the New Account pop-up menu, then choose a type of user.
4. Enter a full name for the new user. An account name is generated automatically. To use a different account name, enter it now—you can’t change it later.
5. Enter a password for the user, then enter it again to verify. Enter a password hint to help the user remember their password.
6. Click Create User.

You can use the article below as a reference.

Add a user or group on Mac

Take care!

Hey there PeterORiordan,

The info from the resource, If your iCloud Contacts, Calendars, or Reminders won’t sync, may help: 

1. “If you store and edit your events in iCloud instead of another place, like On My Mac, Exchange, or Google, then iCloud automatically updates your calendars. If you use multiple accounts on your Mac like iCloud, Gmail, and Yahoo, make sure that iCloud is your default Calendar account:
2. Open the Calendar app.
3. Choose Calendar > Settings. In macOS Monterey or earlier, choose Calendar > Preferences.
4. In the General tab, make sure that one of your iCloud calendars is the default.

If you store and edit your contacts in iCloud instead of another place, like On My Mac, Exchange, or Google, then iCloud automatically updates your contacts. If you use multiple accounts on your Mac like iCloud, Gmail, and Yahoo, make sure that iCloud is your default Contacts account:

1. Open the Contacts app.
2. Choose Contacts > Accounts.
3. Click the iCloud tab. Make sure that you're signed in with your Apple ID and that Contacts is enabled.”

Take care. 

Hi PeterORiordan,

The link in the reply above should help you reach Apple: Apple Support

You can also look for direct contact numbers in this link: Contact Apple for support and service - Apple Support

Take care.

Hello PeterORiordan,

Thanks for checking. For more help, contact Apple Support to investigate this more with you.

Contact Apple Support

Thanks.