Zoho CRM Google Contacts Sync Problem

Zoho CRM Google Contacts Sync Problem

I have syncronised Zoho CRM contacts with Google contacts (two way sync) and now all my Zoho contacts are a mess. Contacts that were linked to Accounts and Sales Orders, Invoices etc are now unlinked and even the email addresses are blank. Any ideas how I can resolve this and why it would have happened. 12,000 contacts and 5 years work in a mess here.