Hi Victor,
You were right, I didn't share enough info, however, among the hints you gave , missing values and column contribution seems to be related to the issue, namely, if there are too many (20 out of 40) columns that were not used by the model (Boosted tree in my case) , the assessment fails , so , as workaround , if I relaunch the analysis taking those columns out, it runs ok...
I will keep on testing to give more feedback,
Thanks!