Small errors in the wp-content/plugins/download-monitor/assets/js/reports/reports.min.js file which is a minified version of reports.js Lines 535 to 550 are like this in the original file:
// Get all dates from the startDate to the endDate
let dayDownloads = dlmReportsInstance.getDates(new Date(startDate), new Date(endDate)),
doubleDays, doubleMonthDownloads, weeksDownloads, weekDownloads;
// Let's initiate our dlmDownloads with something
switch (dlmReportsInstance.chartType) {
case 'months':
// Get double selected months
doubleMonthDownloads = dlmReportsInstance.getDoubleMonths(dayDownloads);
dlmDownloads = doubleMonthDownloads;
break;
case 'month':
// Get selected months
let monthDownloads = dlmReportsInstance.getMonths(dayDownloads);
dlmDownloads = monthDownloads;
break;
Fixed it by making these changes:
// Get all dates from the startDate to the endDate
let dayDownloads = dlmReportsInstance.getDates(new Date(startDate), new Date(endDate)),
doubleDays, doubleMonthDownloads, monthDownloads, weeksDownloads, weekDownloads;
// Let's initiate our dlmDownloads with something
switch (dlmReportsInstance.chartType) {
case 'months':
// Get double selected months
doubleMonthDownloads = dlmReportsInstance.getDoubleMonths(dayDownloads);
dlmDownloads = doubleMonthDownloads;
break;
case 'month':
// Get selected months
monthDownloads = dlmReportsInstance.getMonths(dayDownloads);
dlmDownloads = monthDownloads;
break;