Very Slow Checkout Page

Using the paid version of this plugin on my website, it causes the checkout page to load very slowly. Once you have an item in your basket, it will allow you to go to checkout and it takes 20-30 seconds to load. If I swap over to the free version of this plugin, the checkout loads pretty instantly. Previously, I had to upgrade my server in order to even get the paid version of the plugin to load the checkout page as it would break the site and wouldn’t load the page at all. Any ideas of how I can improve the speed of the loading of the checkout page? The rest of the site is quick.

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