Storefront API - checkoutCreate mutation lineItems variant is null

Shopify Discussion
1

We are seeing this issue when using the checkoutCreate storefront mutation, no errors no issues, but this is what is returned for the checkout lineItems:

"lineItems": {
"nodes": [
{
"title": "Personalized Cartoon Phone Case",
"quantity": 1,
"variant": null
}
]
}

Any ideas? The product is available in the custom app’s sales channel and has not been deleted, the variant is available for sale.

We can also query this ProductVariant node from the storefront api with no issues as well.

Thanks!