Hi Simone,
We have faced issue while enabling DrillThrough in PivotClient (Relational server mode) and we have logged defect report for this issue. And, fix for this issue is estimated to available in our upcoming 2018 Essential Studio Volume 1 Service Pack 2 which is estimated to be rolled out by end of April 2018.
Please let us know if any concerns.
Thanks,
Manikandan.