Thank you for your reply Rishi.
The plugin is working for every child product except the first child product.
I have a Grouped product(simple product) in which I have four child products(all are variable products). The issue is with only the first child product. Variation form is missing or not loading only for the first child product.
All child products are working fine with ajax add to cart, except the first child product because it have no variation form loading.
I don’t know why plugin is skipping the first product to add variation form.