Extract Charts/Graphs as Images from Excel

I am using this activity, and have had some strange results for the output.  

In attended mode (dev environment), it produces graphics for the three charts as expected.  

When moved to the test environment (unattended), the activity creates 6 graphic images from the 3 charts in the excel file.  It creates the 3 expected images with the correct naming convention, then an additional 3 with a different naming convention.  

To add more confusion, when moved to our Prod environment, it now creates 9 images from the 3 graphs.  It creates the 3 expected images with the correct naming convention, then an additional 6 with a different naming convention.  

I do understand the behavior change between the tenants.  I have run VBA on the workbook to count the number of existing graphs, and the result is 3.  What could be causing these results?