Running a recently upgraded instance of Magento CE 18.104.22.168 (from 22.214.171.124). Form key support was built in to the theme and is functioning a-okay when browsing the website with different browsers and caching enabled.
I have noticed however that if a single browser leaves a page open for an extended period of time (roughly 2 - 3 hours), upon resuming activity on that page and clicking the add to cart button does not work the first time it is clicked. The cart is still empty but after a page refresh it becomes functional again.
I'm assuming that this is because the form-key rendered on the page at the time it was generated and output to HTML is no longer the same as what Magento's
core/session model references in the database. After the page refresh this resolves itself.
Has anyone else experienced this? Is there a way to resolve this issue?