From https://confluence.atlassian.com/adminjiraserver071/connecting-jira-applications-to-sql-server-2012-802592195.html :

7. Turn off the SET NOCOUNT option. To turn off SET NOCOUNT:

Which goes on how to accomplish this. Then at the bottom there's this:

• Access the Query Console by right clicking on the newly created database and selecting 'New Query'. Execute the following command to set the isolation level.

ALTER DATABASE THE-NEW-DATABASE-CREATED-FOR-JIRA SET READ_COMMITTED_SNAPSHOT ON

This is a very important step and is easy to miss as currently written.

If we break out the bullet point above into Step 8 I believe this will make the instructions much clearer