Links logging me out.
For instance, if I am logged in and browsing the recent page in desktop view, and I click on a thumbnail, I get taken to the project, but arrive on the mobile site, and not logged in. When I switch back to desktop view, I am still not logged in.
The same happens if I follow a link to a project from a "subscription update" email.
It's not just "arriving on the site and having to log in", if I am already on the site and logged in, then follow a link from an email, the tabs I already have open get logged out as well.
This is using an Android tablet with up-to-date browser.