> The "proxy_cache_path" looks corrupted and incomplete. First of
> all, I would suggest you to make sure you are using "levels"
> parameter, see http://nginx.org/r/proxy_cache_path.

I didn't paste all of proxy_cache_path directive. Here you have all.
proxy_temp_path /cache/tmp;
proxy_cache_path /cache
levels=2:2
keys_zone=my-cache:20000m
max_size=3355443m
inactive=7d;

And also nginx version if needed:

# /usr/local/nginx/sbin/nginx -V
nginx version: nginx/1.5.9