Hyperparameter tuning does not improve accuracy?

I am working on titanic dataset, I achieved 92% accuracy using random forest. However, the accuracy score dropped to 89% after I tuned it using Gridsearch. Now, I was wondering if it caused by imbalanced dataset, since it has only 342 out of 891 passenger survived the disaster. Would appreciate the clarification.

• was the 92% accuracy on the train set or validation set or crossvalidation (or god forbid the test set)? and what about the 89%? – A Kareem May 4 '20 at 15:11