Is there a way to "re-link" all contacts using some button or other procedure?
I did this a few months ago by downloading a third-party contacts app, using its (much smarter) merge function, and then uninstalling the app. I can't remember for sure, but I think the app I used was either Contacts by Contapps or GO Contacts EX. There's also Contact Analyzer 2, but there are some reports of it deleting all contacts instead of merging!