Please don't set the contact sync interval too short, as this may cause your phone to malfunction. This is likely the issue.
Please set this interval to a much longer value, such as 900 (= 15 minutes), and restart your device.
Another issue may be that the system Contacts app is hiding contacts with a certain "Account Type" value. Try searching for them somewhere in the settings (this is a device-specific option, so I can't provide more details).