There was a problem converting the model to onnx format

Vesion

pytorch: 1.6.0

Problem description

The model I use is pointnet++
This is a website with network structure

I only changed the input of the model and changed 9 channels to 4 channels.
For deployment, I want to convert the model to onnx format .
The program has been stuck in torch onnx. export,and model conversion cannot be completed
How can i solve this problem?

Code

model=MODEL.get_model(NUM_CLASSES)

model.load_state_dict(torch.load(checkpoint)['model_state_dict']) 

model=model.eval()

input = torch.randn(1, 4, 768)

torch.onnx.export(model, input, onnx_path,verbose=True,
 input_names=input_names, output_names=output_names,
  opset_version=11) 
print("Exporting .pth model to onnx model has been successful!")

The following is a warning message

Warning

/media/hust/File/wyx/Pointnet2_water/models/pointnet2_utils.py:75: TracerWarning: Converting a tensor to a Python integer might cause the trace to be incorrect. We can’t record the data flow of Python values, so this value will be treated as a constant in the future. This means that the trace might not generalize to other inputs!
farthest = torch.randint(0, N, (B,), dtype=torch.long).to(device)
/media/hust/File/wyx/Pointnet2_water/models/pointnet2_utils.py:75: TracerWarning: Converting a tensor to a Python index might cause the trace to be incorrect. We can’t record the data flow of Python values, so this value will be treated as a constant in the future. This means that the trace might not generalize to other inputs!
farthest = torch.randint(0, N, (B,), dtype=torch.long).to(device)
/media/hust/File/wyx/Pointnet2_water/models/pointnet2_utils.py:293: TracerWarning: Converting a tensor to a Python boolean might cause the trace to be incorrect. We can’t record the data flow of Python values, so this value will be treated as a constant in the future. This means that the trace might not generalize to other inputs!
if S == 1:
/home/hust/miniconda3/envs/PointNet++/lib/python3.7/site-packages/torch/onnx/symbolic_opset9.py:2225: UserWarning: Exporting aten::index operator of advanced indexing in opset 11 is achieved by combination of multiple ONNX operators, including Reshape, Transpose, Concat, and Gather. If indices include negative values, the exported graph will produce incorrect results.
“If indices include negative values, the exported graph will produce incorrect results.”)
/home/hust/miniconda3/envs/PointNet++/lib/python3.7/site-packages/torch/onnx/symbolic_opset9.py:2179: UserWarning: Exporting aten::index operator with indices of type Byte. Only 1-D indices are supported. In any other case, this will produce an incorrect ONNX graph.
warnings.warn("Exporting aten::index operator with indices of type Byte. "