The issue of the National Insurance (NI) category auto-updating to an incorrect letter occurs due to system errors, incorrect data inputs, or updates in employee status that are not reflected accurately.
To resolve this, check the employees' date of birth in Workforce management and compare them against the NIC rules in Payroll.
To check the NIC rules, follow the steps below.
Click Settings, then under UK Tax Rates, click NIC Rules.
Check rules against employees' date of birth.
The Update Only on From Age indicator will only trigger on the employee's date of birth.