Strace is a tool to monitor system calls of an application. The output may be useful to trace what rsyslog is actually doing on the system level, if debug output information is not sufficient.
A quick example to provide useful output would be:
strace -T -ttt -f -o /path/filename rsyslogd
There are a lot of parameters that can be set. For example we can also only monitor system calls related to the network components:
strace -T -ttt -e trace=network -f -o /path/filename rsyslogd
For more details, please visit the man page of strace.