What potential issue can arise from using an external store for Mule application state management?

Using an external store for Mule application state management can introduce additional costs and complexity. When an application is designed to manage its state externally, it typically relies on external systems, which may require additional setup, maintenance, and monitoring compared to an internal store. This reliance can also lead to increased latency, as communication between the Mule application and the external storage system must occur over a network.

Furthermore, managing access, ensuring data consistency, and handling failures or outages associated with the external store can complicate the architecture. Overall, while external stores can enable certain capabilities like data sharing and persistence, they often come with trade-offs that impact both cost and complexity, making this the correct answer.