Displayed correctly when accessing / register, but an error occurs when accessing / files

[e1blue]

I am checking the operation in my environment (CentOS 7, Nginx).
・The top page was displayed normally.
・It was displayed normally when accessing / register.
・However, an error occurred when accessing / files.

Error log

[info] client timed out (110: Connection timed out) while waiting for request, client: IP ADRESS, server: 0.0.0.0:443

What can be considered as the cause?