No fix is required; the system is functioning as designed.
The client continuously runs the compliance check, even when it is not connected to VPN. During that time the client does not know the user name. When the client connects to the gateway again, it sends out all accumulated logs with a user name of "default". Shortly after connecting to VPN again the logs reflect the correct user name, since the client is now aware of the user.
This solution has been verified for the specific scenario, described by the combination of Product, Version and Symptoms. It may not work in other scenarios.