We don't support using offsets (offset_column) in Stacked Ensemble. You can use offsets in the base learners, but Stacked Ensemble metalearner is hardcoded and doesn't honor that. We need to check:
If one of the models used offset_column, that they all use it
If it was used, it must be included in the `training_frame` for Stacked Ensemble and then we should use it automatically.
This column must be copied from the training frame and added to the level-one (metalearning) frame so it’s available for the metalearner to use.