ONNX Runtime static quantization of YOLO11 results in zero mAP metrics

I am trying to quantize the YOLO11 model with onnxruntime, and I have conducted a comparative study of the mAP across all the models I possess: ".pt, onnx, onnx+dynamic, and onnx+static". What I found strange is that in onnx+static quantization, all the YOLO-based metrics are zero (Image). Here is my code:

pt_model = YOLO("best.pt")
dataset = "data.yaml"
PATH = "workplace/models"
workdir = os.path.dirname(PATH)
path_onnx_model = os.path.join(workdir, "best.onnx")
path_preprocess_model = os.path.join(workdir, "prep.onnx")
path_static_quantized_model = os.path.join(workdir, "static.onnx")
path_dynamic_quantized_model = os.path.join(workdir, "dynamic.onnx")
model = YOLO(pt_model, task='detect', verbose=False)
baseline_metrics = model.val(
    data=dataset,
    imgsz=768,
    iou=0.3,
    conf=0.5,
    batch=16,
    device=device
)
pt_model.export(
    format="onnx",
    imgsz=768,
    dynamic=True,
    nms =True,
    conf=0.5,
    iou=0.3,
    batch=16, # expected faster inference
    data=dataset,
    device=device,
)
model = YOLO(path_onnx_model, task='detect', verbose=False)
onnx_metrics = model.val(
    data=dataset,
    imgsz=768,
    iou=0.3,
    conf=0.5,
    project=workdir,
    batch=16,
    device=device
)
shape_inference.quant_pre_process(
   path_onnx_model,
   path_preprocess_model,
   skip_optimization=False,
   skip_onnx_shape=False,
   skip_symbolic_shape=True,
   auto_merge=False,
   int_max=2**31 - 1,
   guess_output_rank=False,
   verbose=0,
   save_as_external_data=False,
   all_tensors_to_one_file=False,
   external_data_location="./",
   external_data_size_threshold=1024)
class ImageFolderCalibrationDataReader(CalibrationDataReader):
    def __init__(self, folder_path, input_name, input_height, input_width):
        super().__init__()
        self.folder_path = folder_path
        self.input_name = input_name
        self.input_height = input_height
        self.input_width = input_width
        self.calibration_images = [f for f in os.listdir(folder_path) if f.lower().endswith(('.png', '.jpg', '.jpeg'))]
        self.current_item = 0

    def get_next(self) -> dict:
        if self.current_item >= len(self.calibration_images):
            return None

        image_path = os.path.join(self.folder_path, self.calibration_images[self.current_item])
        image = cv2.imread(image_path)
        if image is None:
            self.current_item += 1
            return self.get_next()
            
        image = cv2.resize(image, (self.input_width, self.input_height))
        image = image.astype('float32') / 255.0  # Normalize to [0, 1]
        image = np.transpose(image, (2, 0, 1))  # HWC -> CHW
        image = np.expand_dims(image, axis=0)  # Add batch dimension

        self.current_item += 1
        return {self.input_name: image}

    def __len__(self) -> int:
        return len(self.calibration_images)
calibration_data_path = "images"
input_name = 'images'
input_shape = (768, 768, 3)
calibration_dataset = ImageFolderCalibrationDataReader(
    calibration_data_path, 
    input_name, 
    input_shape[0], 
    input_shape[1]
)
quantize_static(
            path_preprocess_model,
            path_static_quantized_model,
            calibration_dataset,
            quant_format=QuantFormat.QDQ,
            weight_type=QuantType.QInt8,
            activation_type=QuantType.QInt8,
            per_channel=False,
            reduce_range=False,
        )
model = YOLO(path_static_quantized_model, task='detect', verbose=False)
static_metrics = model.val(
    data=dataset,
    imgsz=768,
    iou=0.3,
    conf=0.5,
    project=workdir,
    batch=16
)
import onnx
model = onnx.load(path_preprocess_model)
nodes_to_exclude = [
    node.name for node in model.graph.node if node.op_type == "Conv"
]
quantize_dynamic(
    model_input=path_preprocess_model,
    model_output=path_dynamic_quantized_model,
    weight_type=QuantType.QInt8,
    nodes_to_exclude = nodes_to_exclude
)
model = YOLO(path_dynamic_quantized_model, task='detect', verbose=False)
dynamic_metrics = model.val(
    data=dataset,
    imgsz=768,
    iou=0.3,
    conf=0.5,
    project=workdir,
    batch=16
)

No repository file or test is named. Start with the supplied ImageFolderCalibrationDataReader, shape_inference.quant_pre_process, and quantize_static calls, then compare static-model validation with the baseline and dynamic results; done means the cause of the zero metrics is isolated and a reproducible correction or documented explanation is provided.