Contacts

Try going to System Preferences/Apple ID and stop Contacts syncing by unchecking the box. Wait a couple of minutes, then check syncing. Allow time for the sync to complete.

See the Apple Support article below. 

Contacts, Calendars, or Reminders - Get help using iCloud.     

Read these threads why are there separate contacts "on my Ma… - Apple Community

Organizing contacts - Apple Community

You had 2000 contacts these might necessary be in all iCloud , they might be scattered in various groups or in my Mac section , can be created from exchange accounts or they are not properly set up ( having incomplete information ) .

Read Update contact information in Contacts on Mac - Apple Support

Note: If you use an Exchange account, those contact cards can include only three email addresses, and there are limits on the number of phone numbers, names, messaging addresses and street addresses.

If you edit a contact in a read-only account such as Exchange or Google, the changes you make appear only in Contacts.

When you sign in with the same Apple ID on each of your devices and turn on Contacts in iCloud preferences or settings, your contacts are available on all your devices, and changes you make to contacts on one device appear on the others.

Read this article also Set up and use iCloud Contacts - Apple Support

On your Mac

1. From the menu bar at the top of your computer screen, choose Apple menu > System Preferences, then click Apple ID. If you’re using macOS Mojave or earlier, you don’t need to click Apple ID. 
2. Click iCloud.
3. Select Contacts.

All of the information* stored in Contacts uploads to iCloud.

* If you have contacts information stored On My Mac, that information will not automatically sync. In Contacts, drag a contact from On My Mac to All iCloud, or export your contacts as Vcards, then manually sync with the Finder. 

Are you running any anti - virus programs? Using a VPN?

Try setting up another admin user account to see if the same problem continues. The intent is to see if it is specific to one account or a system wide problem. This account can be deleted later. 

Isolating an issue by using another user account 

If the problem is still there, try booting into the Safe Mode using your normal account.  Disconnect all peripherals except those needed for the test. Shut down the computer and then power it back up after waiting 10 seconds. Immediately after hearing the startup chime, hold down the shift key and continue to hold it until the gray Apple icon and a progress bar appear. The boot up is significantly slower than normal. This will reset some caches, forces a directory check, and disables all startup and login items, among other things. When you reboot normally, the initial reboot may be slower than normal. If the system operates normally, there may be 3rd party applications which are causing a problem. Try deleting/disabling the third party applications after a restart by using the application un-installer or by using the developer’s uninstall instructions. For each disable/delete, you will need to restart if you don't do them all at once. 

Safe Mode - About.    

I created this User Tip as a basic framework to manage/recover Contacts - Contacts