It takes too long to create new variants (10 - 15s). $0 item on cart page

[sillycube]

My app is using graphql mutation ProductVariantCreate to create new variants. After a new variant is created, the return variant id is used by cart ajax to add into cart. 

But it takes too long to add into cart. On the cart page, the new variant is showing $0 and no product title.

Since my app is installed by many stores, I can't change the cart liquid. Look like it is a Shopify backend issue

Any fix?

You can find the screenshot in Another related thread

[sillycube]

bumps