401(a) supplemental retirement benefit stopped deducting on employee paycheck

Summary

401a employee benefit stopped being deducting (which should not have happened) and we are not sure why

Content

An employee contributes $1,800 towards a 401a supplemental retirement account every pay period.  A couple pay periods ago, this contribution inadvertently was $484.11 and subsequently no deductions were made.  In looking at Oracle we are not sure why this happened.  We have a cap on the benefit element of $56,000 annually which the employee is not close to reaching.  We are trying to see if there may be a limit set on the payroll element but are not sure where to find that.  Any clues as to why this amount turned off and if there is a way to manually