If it happens again have the operator responsible for setting up and running the machine visit the customer to explain what happened.
To the OP - I'd say if you haven't done so already, open a Corrective Action and really get to the root of the issue. This is especially valid if you're ISO certified. Section 8.7.1 of the 2015 standard states: "The organization shall ensure that outputs that do not conform to their requirements are identified and controlled to prevent their unintended use or delivery.
Just my
.