If you are using the "W3 Total Cache" plugin, you may encounter some issues when visiting the checkout. This is due to aggressive page caching (which is a good thing!), but it can be easily resolved by excluding the checkout page URL from the cache plugin.
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 “W3 Total Cache” and click on the "Page Cache" link.
Step 3: Scroll down below to the section until you see the ‘Never cache the following pages’ option
Step 4: To exclude "checkouts" pages enter your noted checkout page slug (from step 1) with special characters as shown in the screenshot: "/checkouts*"
Step 5: Click on "Save all settings".
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.
If you are creating any Embed Form or using CDN or Varnish cache, you just need to exclude the URL in the cache plugin's exclude settings.