Ok, i have found the problem.
In fact, this came from apache2 with mod_proxy.
Before, the apache config file contains :
ProxyPass / http://localhost:8200/
ProxyPassReverse / http://localhost:8200/
I had this line
AllowEncodedSlashes On
And now it works 
See this post : Reverse Proxy on NGINX - #7 by jesjimher