I resolved this issue but it is probably not "best practice" to do what I did.
What I was doing was going into the release to edit the task. In the screen on the right is the override template parameters which is where I was adding the dbconnxion string. I tried both the <server>.database.windows.net and the full connection string from the "show database connections strings" in the database blade. Neither worked.
So then I went into the adf_publish branch and edited the ARMTemplateforFactory.json file - change the server name to production and then redployed the failed release successfully.
Not quite as elegant a deployment as I had hoped but it worked.