We're having a strange issue on our client's shops after applying the SUPEE-9767 patch and updating the theme files.
Apparently many of their customers are using Chrome, which is caching the old form, and the form-key is not being submitted. This results in the checkout process halting after entering the CC information.
We're sending the following headers:
Expires: Thu, 19 Nov 1981 08:52:00 GMT Cache-Control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0 Pragma: no-cache
...but it looks like Chrome is ignoring them.
Anyone else experienced this issue?