Sorry, you are correct. feature_importances works properly in the research environment for RadomForestClassifier. The issue seems to not be directly related to parallelization, but to the use of serialization by feature_importances implementation. The IDE environment has stricter restrictions regarding serialization than the research environment.
Another community member ran into the same problem with RandomForestsClassifier, but reported GradientBoostingRegressor feature_importances working fine in the IDE environment.
Unfortunately, we do not have a timeline yet for these improvements, but it is definitely on our radar.
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