Coinbase changes addresses as you'll know.

Here are a list of mine in the past. It looks as if the recipient address of my bitcoin was none of them. How would this have happened? 1, I somehow scanned the wrong QR code? 2, I was infact a victim of a phishing hack? 3, that address has something to do with the original shapeshift attempt.

Each account on Coinbase is a collection of addresses. New addresses are automatically generated for each payment on Coinbase and stay associated with your account forever (so it is safe to reuse them).
 
bitcoin address

Address   Label   Created   
1CvWXwVowhRFi4TbU6miFvZcrNGT64T9Au
3 minutes ago   Details

14BguFGySJrEDTdmuggfZ7qH7gucSaDZgF
about 19 hours ago   Details

16frfsCefQ8G6GGXM7dYfvgbHvw7woLS1v
12 days ago   Details

1AtAYxjLetGrHVpDRbdnSpPnA3o5ohTNUE
15 days ago   Details

1FHk5w9E5A1Rkjc1AZK3ymQu7u5aQUCpzs
15 days ago   Details

178t7tUH8GpsQYVjmcGQXUTLWZzJNrXnqG
17 days ago   Details

14Jo7d32rcWxzUV1x6Z5zPm6EPFsntLiBZ
17 days ago   Details

1NBgUecvmWRGQ3xNSBQQU3WHeYQQEZZKwi
17 days ago   Details

1FnnCerMTsnKs9niAqZfudGWdnhEn74QeB
17 days ago   Details

1DvQP5Ei7h9t2ZHF29bo4sCN3PLRird7nx
4 months ago   Details