If you are using “Hummingbird Page Speed Optimization” plugin, you may encounter some issues with AeroCheckout 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 “Hummingbird” and click on Caching menu under it.
Step 3: Select the “Page Caching” tab.
Step 4: Locate for the option “Exclusions” below.
Step 5: To exclude “checkouts” pages enter your noted checkout page slug (from step 1) as shown in screenshot: */checkouts/*
Step 6: Scoll down the page and click on “Save Settings” button to update the changes.
Note: By default, AeroCheckout pages slug is “checkouts”. If you had changed the checkout pages slug for any reason get the slug from here AeroCheckout > Global Settings > Miscellaneous tab > Checkout Page Slug