Adding bundle product to cart using rest API facing issue

Below is my rest API,

if the last child item option qty is greater than 1, for example 2 then the bundle quantity added to cart is 2. Below is my API request

{
    "cartItem": {
        "qty": 1,
        "quoteId": "99264",
        "sku": "testbund2",
        "product_option": {
            "extension_attributes": {
                "bundle_options": [
                    {
                        "option_id": 9,
                        "option_qty": 1,
                        "option_selections": [
                            17
                        ]
                    },
                    {
                        "option_id": 10,
                        "option_qty": 1,
                        "option_selections": [
                            18
                        ]
                    },
                    {
                        "option_id": 11,
                        "option_qty": 2,
                        "option_selections": [
                            19
                        ]
                    }
                ]
            }
        }
    }
}

The response I get is below:

{
    "item_id": 86590,
    "sku": "testbund2",
    "qty": 2,
    "name": "Bundle product 2",
    "price": 4705,
    "product_type": "bundle",
    "quote_id": "99264",
    "product_option": {
        "extension_attributes": {
            "bundle_options": [
                {
                    "option_id": 9,
                    "option_qty": 1,
                    "option_selections": [
                        17
                    ]
                },
                {
                    "option_id": 10,
                    "option_qty": 1,
                    "option_selections": [
                        18
                    ]
                },
                {
                    "option_id": 11,
                    "option_qty": 2,
                    "option_selections": [
                        19
                    ]
                }
            ]
        }
    }
}

But If I set default child qty to 1 for last child,
The response looks ok.

Request with last child qty as 1 is:

{
    "cartItem": {
        "qty": 1,
        "quoteId": "99264",
        "sku": "testbund2",
        "product_option": {
            "extension_attributes": {
                "bundle_options": [
                    {
                        "option_id": 9,
                        "option_qty": 1,
                        "option_selections": [
                            17
                        ]
                    },
                    {
                        "option_id": 12,
                        "option_qty": 1,
                        "option_selections": [
                            23
                        ]
                    }
                ]
            }
        }
    }
}

Response is

{
    "item_id": 86669,
    "sku": "testbund2",
    "qty": 1,
    "name": "Bundle product 2",
    "price": 2100,
    "product_type": "bundle",
    "quote_id": "99264",
    "product_option": {
        "extension_attributes": {
            "bundle_options": [
                {
                    "option_id": 9,
                    "option_qty": 1,
                    "option_selections": [
                        17
                    ]
                },
                {
                    "option_id": 12,
                    "option_qty": 1,
                    "option_selections": [
                        23
                    ]
                }
            ]
        }
    }
}

Can anyone help me what is the issue. I checked and disabled all the custom plugins and observer related to this. But still issue exists. I a trying to fix this for last 2-3 days.