HESA Record Validation Check Person.STAFFID.8 failed

What causes this issue?

If a member of staff was included in last year's Staff return, where any
contract record for this person has (any Activity.ACTSOC major group 1,
2 or 3 and Contract.TERMS = 1 or 2 and Contract.ENDCON does not exist)
and Person.DATELEFT does not exist in last year's return, then a record
must be included in this year's Staff return.

System Response

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

How to fix this error?

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.