I'm having a similar issue with using Stepper in accessibilityRepresentation.
When I use Stepper outside of the representation, I get access to increment and decrement button, as seen in the console screenshot here. When it's within .accessibilityRepresentation the automation tests only register the QuantityStepper accessibilityId and the QuantityStepper-Decrement and QuantityStepper-Increment buttons aren't available.
I think accessibilityRepresentation would give the user the best experience, but this is preventing me from using it.