As far as I can tell, CMIO system extensions run under the system user _cmiodalassistants, which does expose the XPC services correctly. You can verify this by checking the exposed endpoints for that user:
sudo launchctl print user/262
The problem, it seems, is that the user session (which launches the main application) does not have access to the endpoints exposed by _cmiodalassistants, resulting in the error you are seeing.