Redmine

I had repos browsing and was about to click 'download' to check a file locally.
Then I went on to something else, and came back long enough to the session to time out.
On the open page, with the file being displayed, I clicked the 'Download' link to get the file.
I was presented with a completely empty white page.
Going 'back' and clicking somewhere else I (correctly) got the familiar (re)login page.

'Autologin' disabled.
What info is required to understand this?

(couldn't find a fitting category, no session or authentication related categories)