If you are using the "Breeze" Plugin by Cloudways, you may encounter some issues with empty carts when running the offer pages. 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 offer page.
You need to exclude offer pages by following these instructions:
Step 1: Note down the slug of your offer page from the general settings
Step 2: Open the settings of "Breeze" under the Settings tab.
Step 3: Jump on the "Advanced Options" tab.
Step 4: Locate the option "Never Cache these URLs"
Step 5: To exclude “offer” pages enter your noted offer page slug (from step 1) as shown in the screenshot:
Step 6: Click on the Save Changes button to save the settings.
By default, the upsell pages slug is "offer". If you had changed the offer pages slug for any reason get the slug from FunnelKit (formerly WooFunnels) > Settings > General > Permalinks.