Lost contacts

If you are syncing Contacts with iCloud, try going to System Preferences/iCloud and stop Contacts syncing by unchecking the box. Wait a couple of minutes, then check syncing. Allow time for the sync to complete.

Contacts, Calendars, or Reminders - Get help using iCloud

Last resort  - have you tried signing out of iCloud and then sign back in?

See these articles https://support.apple.com/en-bw/HT205754

https://support.apple.com/en-in/HT203521

See this thread https://discussions.apple.com/thread/8564027