If a module's onUnload tries to do anything that uses a CF mapping for that module such as asking WireBox for a CFC instance, it will error when you fwreinit. This is because the ColdBox bootstrap calls reloadChecks() BEFORE it adds module mappings. We need to load up module mappings prior to shutting down the framework so that all shutdown code can work correctly.
To reproduce this, install cbelasticsearch and fwreinit. I assume most people worked around this by just creating a manual CF mapping which masked the issue.