Can't connect via RCON after a period, plugins not reloading

Im using AWS EC2 r4.large, centos7 for my rust dedicated server.
I created rust dedicated server by using LGSM.
By typing ./rustserver start, I can start up my rust server.
My server is opened completely. it seems there is no problem.
i can connect webrcon provided by facepunch, rust:io map(http://MyServerIP:GamePort), etc..
but after 5 minutes, I cannot connect webrcon, rust:io,
and it seems every tcp port is closed.
On rusty administration tool, it said Not connected.
so, I cannot use EnhancedBanSystem, PlayerDatabase plugin by MySQL..
and in-game F1 console didnt respond.
and when i try reload a plugin, it didnt respond too.
so i try reload one more time, but it said "Reload requested for plugin which is already loading: [plugin name..]"

How can I fix it?

P.S. OS is centos7 AMI provided by aws, iptables&firewalld is deactivated now.
on my aws security group, i had opened my game port 28015(udp/tcp), webrcon port 28017(tcp),
but it isnt effective, so i opened all tcp/udp port.
BUT it isnt effective too.