Check the 'context' for the sub_filter directives you are trying to
use. They do not say they can be used with 'if'.
http://nginx.org/en/docs/http/ngx_http_sub_module.html
Also worth reading about using 'if':
https://www.nginx.com/resources/wiki/start/topics/depth/ifisevil/
_______________________________________________
nginx mailing list
nginx@nginx.org
http://mailman.nginx.org/mailman/listinfo/nginx