Please check if you can see the IR8S record in Income Tax module, under Process, View Tax Record. You should have two records e.g. Current IR8A and IR8S. If the IR8S record is missing, you need to review the whole year's pay record as below:
Check the employee hire and cessation date, if there is rehired employment. If the employee has payroll record in the system for the period they are not employed then system will not be able to generate IR8S.
Check the employee hire and cessation date for all the employment against with the statistic report.
Change the hire or cessation date if it is wrong or if the pay record not valid or not suppose to be there, delete the pay record if necessary.
If above steps not resolved then please try as follows:
Go to Payroll module and click Pay Record
Check from period 1, and double-click the affected employee
Check all the pay elements and deduction dates, they should be in the year of the income tax assessment year.
You need to check for the whole year of pay records month by month and amend the date if required.