Sometimes a trace is needed called a listener trace. This trace can only be created by setting up traces in the ini file and restarting the agent. Then a file with a name like:
With 21.0.8, this file is not created.
This is caused by a defect in the code
There are some service packs that did not correctly create the listener trace. Update the agent to 21.0.9 and the correct files will be created.