If you host your site on "SiteGround" and using the "SG Optimzer" Plugin, you may encounter some issues with empty carts when visiting the checkout page. This is due to aggressive page caching (which is a good thing!), but it can be easily resolved by requesting that WP Engine set up a special cache exception for your checkout page.
You need to exclude checkout pages by following these instructions:
Step 1: Note down the slug of your checkout page from the general settings
Step 2: Open the settings of "SG Optimizer".
Step 3: Locate the option "Excluding URLs" on the left side.
Step 4: To exclude “checkouts” pages enter your noted checkout page slug (from step 1) as shown in the screenshot: checkouts/*
Step 5: Click on Exclude button to add this slug as an exclusion.
Step 6: Here is the final output slug added of the checkouts page to exclude from the cache.
Note: By default, the Checkout page's slug is "checkouts". If you had changed the checkout pages slug for any reason get the slug from FunnelKit (formerly WooFunnels) Settings > General > Permalinks.