luceos
There was a problem with nginx configuration. I'm going to Dockerize Flarum and fastcgi need these parameters to work properly with Flarum :
fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
fastcgi_param SCRIPT_NAME $fastcgi_script_name;
I think you should add some default docker configurations for Flarum. Maybe I can help you, because I already did the same thing.
Do you have any plan to do that ? I can send a PR ...