The AsyncGenerator tool creates an Async version of private static SQLite20Driver.Connection_StateChange().
However, it isn't used in CreateConnection(), but it has a follow-on effect of generating Async versions of everything that uses DriverConnectionProvider to no real effect.
In the SQLite20Driver, this is the CreateConnection() that doesn't use the async event handler:
If this StateChange event handler can be fire-and-forget, then the Connection_StateChange will be "async void", and should be manually changed to use ExecuteNonQueryAsync (not have a duplicate function).
This might be considered a bug in AsyncGenerator in that it's generating an unusable private event handler.
In the mean-time, I've started a pull request. https://github.com/nhibernate/nhibernate-core/pull/712