Creating an issue in gitlab-ce results in a 405 Method not allowed

Hi all,

I’ve managed to migrate gitlab 8.1 to 8.2, but I get an annoying issue.
Everytime I try to create an issue, I get this error :


==> /var/log/gitlab/gitlab-rails/production.log <==
Started POST "/api/api/issues" for 93.93.xx.xxx at 2015-12-15 15:05:13 +0100

==> /var/log/gitlab/nginx/gitlab_access.log <==
93.93.xx.xxx - - [15/Dec/2015:15:05:13 +0100] "POST /api/api/issues HTTP/1.1" 405 2 "https://git.myhost.name/api/api/issues/new?issue%5Bassignee_id%5D=&issue%5Bmilestone_id%5D=" "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/47.0.2526.80 Safari/537.36"

It only occurs on this project. Do you have any idea where it comes from ?
For information, I use a custom nginx

Thanks,

Edit: To give more details, I have a white page like this when creating the issue :

screenshot-git.payname.tools_2015-12-15_21-28-24