A team writes a MessageDispatchInterceptor to reject invalid commands, but the checks never seem to actually run in production. What is the most likely cause?

The most likely cause is that the interceptor class was written and implements MessageDispatchInterceptor correctly, but was never actually registered with the CommandBus via registerDispatchInterceptor(). This is a common and genuinely silent mistake: there's no compile error and no obvious runtime warning, since Axon has no way to discover an interceptor on its own — registration has to happen explicitly, typically inside a @Configuration class that injects both the CommandBus and the interceptor. Without that registration step, the interceptor simply never gets invoked, and commands that should have been rejected pass straight through to the aggregate untouched. The fix is to confirm the registration code actually runs at startup, and to add a simple log line inside the interceptor during testing to verify it's firing, rather than assuming correctness just because the class compiled cleanly.