apache - Why is there a loading lag when I open a website on a local area network? But it doesn't work when opened locally on the server?-PHP Chinese Network Q&A

Webpage 1:

Webpage 2:

Found that the slowness is mainly caused by the download of the homepage.
(But if you download from this server, you can directly enjoy the Internet speed of 100Mbps.)

Network environment: Unit LAN environment

系统环境：（已yum升级到最新版本） CentOS 7 x86_64 2.1511.el7.centos.2.10 Apache 2.4.6 php 7.0.0 mariadb 5.5.44

Hardware configuration (virtual machine):
8-core CPU
4G memory
Hard disk IO read performance exceeds 250MB/S

When loading the website, part of the css and js will be loaded first, then it will freeze for a few seconds, and then the remaining css and js will be loaded. As shown above. It takes a while to fully open.

but! ! !
If I use http proxy, go to this server and then access it. There is no such phenomenon at all when opening a web page, it opens instantly. (About 1 second)
[This eliminates problems caused by apache, php, mysql configuration, memory overflow, and hard disk IO speed]
However, I searched for a long time and couldn't find the problem.