Re-run 'matched contacts suggestion'
I don't know the exact answer, but you can always manual link contacts, which is a workaround I use,


In Contacts, open one contact, then click the broken clip icon in the top-right corner (I am using Sensation XE).
In the pop up screen, choose all contacts
Search for the one you want to link to and click it


Then the two contact items are linked if you click Finish. You can click Cancel if you don't want them to be linked.