Hi,
it seems, logwatch is not executed while the agent is running. Please check, that mk_logwatch.py in /usr/lib/check_mk_agent/plugins is owned by root and has chmod 755 set.
After this, please run
check_mk_agent > /tmp/out
an take a look in the output file. Search for al section named
<<<logwatch>>>
If this section is missing the plugin is not working. If the section is there but empty then there is a problem with your /etc/check_mk/logwatch.cfg.