How to solve error "too_many_lines"?

Determine the related field that is causing this with awk -F= '{print $1}' /var/log/lynis-report.dat | sort | uniq -c | sort -b -n | tail -3 | sort -r -n

This command will show the three most repeated lines. Use the grep command to find the related test. If the test starts with "PLGN", perform the grep in your PLUGINDIR (lynis show plugindir), otherwise use the INCLUDEDIR (lynis show includedir).