Fields with @propertyWrappers are not being read

The following model (from Vapor FluentKit) works fine with codable routes,

final class Person : Model {
    static let schema: String = "person"

    @ID(key: "id")
    var id: Int32?
    @Field(key: "first_name")
    var firstName: String
    @Field(key: "last_name")
    var lastName: String

    init() {}
}

but returns blank fields when using templates (Stencil). No errors are thrown and I get the same behavior using context: [String: Any] or codable render methods.