Feature importance with scikit-learn Random Forest shows very high Standard Deviation
You are using RandomForest with the default number of trees, which is 10.
For around 30 features this is too few. Therefore standard deviation is large. Try at least 100 or even 1000 trees, like

clf = RandomForestClassifier(n_estimators=1000)


For a more refined analysis you can also check how large the correlation between your features is.