Hi, I know this post is too old, thought it might help someone else in future. I had a similar issue.
1. Update the app.cfg located at "C:\Program Files\SASHome\DataFluxDataManagementStudio\2.6\etc" with below line
java/command="C:\Program Files\Java\jre1.8.0_172\bin\java.exe" -Xms108M -Xmx250M
For options looks at the documentation XML node section https://support.sas.com/documentation/onlinedoc/dfdmstudio/2.7/dmpdmsug/Content/dfU_FAQ.html
2.But I found that once you add fields and by changing Maximum number of row on return from 0 some number or blank. It works.
