Oracle File watcher - diagnostic

Filewatcher is a new scheduler object with job triggered by the arrival new file in specified location.
I don't want describe configuration, but how to get more information about how it's work.
Normally, there is no information why sometimes files are not processed. I have not found the table with logs.

For more information, we must enable trace level on database: 

alter system set events '27401 trace name context forever, level 262144';

After that our instance will create trace files for all new files in filewatcher location.

To diable this trace we have to do:

alter system set events '27401 trace name context off';