I just checked the error log and it looks like this:
[code]
2017/04/23 19:30:48 [error] 20219#0: *1 upstream prematurely closed connection while reading response header from upstream, c$
2017/04/23 19:30:48 [error] 20219#0: *1 open() "/www/subdomain.domain.com/aism/50x.html" failed (2: No such file or directory$
[/code]
[code]
2017/04/23 19:30:48 [error] 20219#0: *1 upstream prematurely closed connection while reading response header from upstream, c$
2017/04/23 19:30:48 [error] 20219#0: *1 open() "/www/subdomain.domain.com/aism/50x.html" failed (2: No such file or directory$
[/code]