Signal peaking on the wrong side?

Hello,
I send you the original dataset, because I failed to produce for you a smaller test sample:
https://cernbox.cern.ch/index.php/s/2ZpW3V8o7aG8DYH

The factory book parameters I used for the BDT are:
“!H:!V:NTrees=1000:MaxDepth=2:MinNodeSize=2.5%:nCuts=20:BoostType=Grad:UseBaggedBoost=true:Shrinkage=0.1:BaggedSampleFraction=0.5”

Let m know if you need more information.
Luca.