With new installations of MySQL and certain configurations set in MySQL, you may receive the following message from SimpleRisk in your Apache error log file:

[Sat Dec 24 11:29:18.609369 2016] [:error] [pid 21351] [client 192.168.0.1:50520] PHP Fatal error:  Uncaught exception 'PDOException' with message 'SQLSTATE[42000]: Syntax error or access violation: 1055 Expression #1 of SELECT list is not in GROUP BY clause and contains nonaggregated column 'simplerisk.risks.submission_date' which is not functionally dependent on columns in GROUP BY clause; this is incompatible with sql_mode=only_full_group_by' in /var/www/simplerisk/includes/reporting.php:2129\nStack trace:\n#0 /var/www/simplerisk/includes/reporting.php(2129): PDOStatement->execute()\n#1 /var/www/simplerisk/reports/index.php(103): risks_by_month_table()\n#2 {main}\n  thrown in /var/www/simplerisk/includes/reporting.php on line 2129, referer: https://myhost/index.php

This is because SimpleRisk currently does not support "only_full_group_by" mode for MySQL which is currently set for your instance.  

To unset that value without clearing any other sql_mode values, use the command:

SET sql_mode=(SELECT REPLACE(@@sql_mode, 'ONLY_FULL_GROUP_BY', ''));

To permanently disable the only_full_group_by SQL mode, edit the /etc/my.cnf file and look for a line that reads "sql_mode=".  Make sure that "only_full_group_by" is not set.  If it is, remove it, and restart your mysql server.

More details on fixing this issue can be found here.