Currently, when async engine is shutting down or already shut down, IllegalStateException is thrown. Consider to throw more specific exception derived from DebeziumException to be able to clearly identify this is the case based on the exception type. This may be handy e.g. in Debezium server shutdown hook to safely skip such exception.
However, to be visible to external modules/projects like Debezium server, it would have to be added to Debezium API and not sure it it worth the such change.