There are a few reasons this could happen.
can you verify the concurrency isn't being overridden on the factory, such as in code with a factory.setConcurreny("10") or something like that?
Do you maybe have multiple @JmsListeners in different classes or configs or even another instance of the app listening to the same queue?
If it's neither of those can you share more info around what your app looks like? Are you using Solace's JMS starter? or something else?