`fx.export_and_import` hangs

I have a simple program:

class Conv2D(torch.nn.Module):

    def __init__(
        self,
        kernel_size=3,
        in_channels=8,
        out_channels=16,
        stride=1,
        padding=0,
        dilation=1,
        bias=True,
    ):
        super().__init__()
        self.conv = torch.nn.Conv2d(
            in_channels=in_channels,
            out_channels=out_channels,
            kernel_size=kernel_size,
            stride=stride,
            padding=padding,
            dilation=dilation,
            bias=bias,
        )

    def forward(self, x):
        return self.conv(x)

if __name__ == "__main__":
    model = Conv2D(
        kernel_size=(3, 3),
        in_channels=3,
        out_channels=8,
        stride=(1, 2),
        padding=(1, 1),
        dilation=(1, 1),
        bias=False,
    )
    model.eval()  # Set to evaluation mode
    example_input = torch.randn(2, 3, 5, 32, requires_grad=True, device="cpu")
    prog = torch.export.export(model, (example_input,))
    torch_module = fx.export_and_import(
        prog,
        func_name="temp",
        enable_graph_printing=False,
        import_symbolic_shape_expressions=True,
    )
    print(torch_module)

When I run it, it can generate the Torch-MLIR module like I want. However, when the program finished, it didn't exit cleanly but rather just hung there. I had to Ctrl+C to exit. I found the same thing happens to one of the examples - projects/pt1/examples/fximporter_resnet18.py (I've not checked other examples).
I've tried running my program with a debugger, and it looks like at the end, some Python internal cleaning processes got stuck in a loop or something like that. I'm not entirely sure what causes that.