I had a similar problem a few minutes ago. I had literally hundreds of duplicates for two of my contacts. When I selected any of them, nothing opened except for a tiny message saying "The contact doesn't exist." I couldn't erase them.
I read this: http://www.anushand.com/2015/04/my-nexus-5-couldn-connect-calls-with-my.html
and tried what they suggested (uncheking the contact syncing boxes of all accounts from the Accounts section in the Settings), but it did not work.
What I had to do is go to the Outlook app and THERE uncheck the contact syncinc box. Now everything seems to work fine, all the duplicates are gone.
I'm not sure if I had to uncheck both boxes, the one from the Accounts section in the Settings AND the one directly from the app, in order for this to work. Maybe only one of them is buggy.
Anyways, right now I'm not taking chances: I'm only syncing Google contacts.
I have a Nexus 4, 5.1.1.