Have you recently added new equipment/services/labor to your existing agreement? Was the equipment/services/labor added on a coterminous basis?
Adding on a coterminous basis will allow you to add new equipment/services/labor such that both the original agreement and the addendum will terminate at the same time. However pricing may be higher, depending on the length of time remaining on the existing agreement, since the costs for any additions would need to be spread out over a shorter period of time.
If the amendment/addendum was not coterminous with the current agreement you may be subject to liquidated damages and fees should you terminate the agreement in accordance with the terms on the master agreement. Also, be mindful if any amendment/addendum extends the term of the master agreement.