It's distressingly common for JS developers to just throw something like "t.track('payment')" in the onclick handler for the last button (or every button) in a payment flow, where "t" is some analytics package you've blocked. No exception handling, of course, so when the analytics package isn't loaded, nothing happens when you click the button. If you're lucky, there will be a console message logged saying something like "unable to call method track on undefined".