with the new January 2019 release it is not possible to apply the "Group by" step to your Oracle data source anymore (see screenshots). Problem can be reproduced on different servers, databases, tables and computers.
This is a massive show stopper for us as we have many users using Oracle as a source in Power BI.
Can you please look into this issue? Thank you! :-)
Select Group by on a column in PQEClick OKAlways receive this error, tested it on different servers and databases