Bad gateway error on Raspberry PI with Nginx


I’m currently re-installing my Raspberry PI after a trouble.
I’m trying re-install Seafile server and I get a 502 Bad gateway error.
My seafile version is 8.0.3.
It runs behind Nginx. For the moment I try to acces seafile from the root of my domain to be as close as possible from the description in the manual. (from port 80 only for the moment).
Nothing in the forum messages could fix my problem.
Seahub error log is : upstream prematurely closed connection while reading response header from upstream, client:
I can post some other logs / info that could be of interest.
Thanks in advance for your help.