Background on the problem
I have a WooCommerce site hosted on WPEngine. Before going live, I contacted support with a list of pages to exclude from caching. I tested the checkout functionality, everything worked fine.
Yesterday I checked Google Analytics and noticed that not a single Chrome user proceeded through the funnel to the checkout page after adding to cart. Panicked, I started investigating.
It turns out that add to cart doesn't work only in Chrome and only when not logged in. By doesn't work, I mean that the page reloads with the ?add-to-cart=xxx string, but the cart is empty - exactly what happens when the caching isn't disabled. Tried Chrome on different PCs, clearing browser cache, but the problem was reproduced on each PC exactly the same.
I thoroughly tested my site before launch in all desktop and mobile browsers. I never caught this problem because Chrome is my day-to-day browser and I'm always logged in.
What caused this problem?
I submitted a ticked about this yesterday and got a reply today stating that "this is actually a common issue" and I needed to provide them with a list of pages to exclude from caching (which was already done). The problem has also mysteriously disappeared.
Is this truly a common problem? Before submitting the ticket, I googled it, searched WordPress forums, this stack exchange, but came up with nothing.
It may be fixed, but I'd like to know what could've caused this. Can anyone shed any light on this?