Alright after about a whole day of near-continuous downtime I finally found the bug that I overcame few months ago already. I’m using nginx as proxy to Django per FCGI. Now after upgrading nginx the site started to misbehave. No matter which location I tried to access I always ended up on the index page.
So after loads of trial and error I came to the conclusion that the problem is in the fastcgi_params file. Consider this line:
fastcgi_param SCRIPT_NAME $fastcgi_script_name;
What Django expects is not SCRIPT_NAME but PATH_INFO:
fastcgi_param PATH_INFO $fastcgi_script_name;
So in case you ever wonder why your Django app only shows you the index page no matter which URL you try to access this might just have to do with the FCGI params.