Simple Voter Class Error - TypeError: Cannot cast array data from dtype('O') to dtype('int64') according to the rule 'safe'

After creating a pipeline with my best models and including the feature-transformer I used to create the training data… I get the following error:

TypeError: Cannot cast array data from dtype(‘O’) to dtype(‘int64’) according to the rule ‘safe’

My feature pipeline makes use of StandardScaler, OneHotEncoder, HashingVectorizer and uses make_column_transformer to make a Pandas column transformer.

ensemble_pipeline = make_pipeline(
    feature_pipeline,
    SimpleVoter(
    best_models, 
    classes=best_models[0][1].classes_, voting="hard"
    ),
)

Any idea the reason behind this error?

Thanks!