When registering agents and using the -u switch it does not enable the agent to take live updates.
This is by design the '-u' switch tells the Manager that the agent is able to take live updates.
This is a legacy feature from ESM/MBC.
To enable live update on the agent, this is done during agent installation using the esmsetup Phase 14.
After install you can run the esmsetup interactively to enable live updates.
Or you can manually create the /esm/config/liveupdate.dat file, an empty file will enable live updates on the agent.
Running the following command as root user will also enable live update.