That is very strange - the other months do work (
http://dev.jagqld.org.au/index.php/calendar/monthcalendar/2017/10/-?jEV=flat)
I don't see how $this->datamodel->getPrecedingMonth($this->data); can return a null - it will either return an array of data or a false.
in the getAdjecentMonth function in components/com_jevents/libraries/datamodel.php at line c. 1117 find the code
if ($year>$latestyear || $year<$earliestyear){
return false;
}
and replace it with
echo "year = $year latest = $latestyear earliest = $earliestyear<br/>";
if ($year>$latestyear || $year<$earliestyear){
return false;
}