The generator converts fields of array types, such as uint16_t[6] to a List (in FieldGenerator.arrayType()), however ReflectionPayloadDeserializer.deserialize doesn't have a case for this.
I would also recommend adding a warning print at the end of ReflectionPayloadDeserializer.deserialize if there is no type match, so at least it's made obvious to the user that something is wrong, instead of just having a null field.