We have items in both Incoming Timesheet Images Timesheet Validation but when I run a Timesheet Chaser report none of these names appear - why is that?

The Timesheet Chaser Report will only detail timesheets that are late, i.e. with a Period End date later than the current day.  

If the Period End date on those timesheets is later than today they will not qualify for a reminder as they are not technical late yet.