Personal Expenses Mileage Rate Issue in Oracle 11i

We have recently created a new mileage rate schedule for tax year 2019-2020. In the mileage schedule, we have thresholds of  up to10,000 miles and 10,000 miles and above.

We have different rates for the two thresholds, however for one of the vehicle types even though threshold has not been exceeded personal expenses are being adjusted to the lower rate after expenses claim has been approved. Has anybody encountered a similar problem and what was the cause?