hi P.J.
You are doing exactly right.
Some metrics are more expensive to be calculated, need to be enabled by passing compute_oob_variable_importances=True. See list of flags here 3.
Please let me know if this helps.
But odd indeed, when I turn off compute_oob_variable_importances (I usually have it enabled), I do get the following keys: ['NUM_AS_ROOT', 'MEAN_MIN_DEPTH', 'NUM_NODES', 'SUM_SCORE'].
Are you doing regression or classification btw ?