Perhaps this applies? In the June 2017 version Release Notes under Known issues and limitations:
Qlik Sense tables and charts with columns with duplicate IDs are not supported
Jira issue ID: OP-3858
Qlik NPrinting Designer does not support Qlik Sense tables and charts that contain two or more
columns with the same ID (columns that refer to the same field). If you try to add a Qlik Sense table or
chart with a duplicate column, the following error message appears:
An item with the same key has already been added.
You must remove the duplicate columns from the Qlik Sense tables and charts, and then reload the
cache of the connection to the Qlik Sense app that contains the modified tables and charts.
HTH - Daniel.