I have the Classic theme selected (because I find it easier to scan), and sometimes the site shows me a stories list page without applying the theme. (For example, there are no boxes around any of the stories, and the data is laid out in a different format than I am used to.)
When that happens, it's usually very difficult for me to force the site to show me the page in the Classic theme (many iterations of Force Reload in Chrome). But if I'm looking at (for example) the New Stories page, it usually corrects itself when I go to another page, but when I come back to the original page it will remain broken. This used to happen once in a blue moon, but recently it has been happening multiple times each week.
I'm using the latest version of Chrome.