If you are using "Comet Cache" plugin, you may encounter some issues with Aero/the Funnel Builder Checkout page 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 URI from cache plugin.
You need to exclude checkout pages by following these instructions-
Step 1: Note down the slug of your checkout page from here
Step 2: Open the settings of “Comet Cache”
Step 3: Jump on "URI Exclusions" tab.
Step 4: To exclude "checkouts" pages enter your noted checkout page slug (from step 1) with special characters as shown in screenshot: "^/checkouts/**"
Step 5: Click on "Save all changes".
Note: By default, Checkout page's slug is "checkouts". If you had changed the checkout pages slug for any reason get the slug from Global Settings > Miscellaneous tab > Checkout Page Slug