icestate is very often disconnected

I use janus.plugin.videoroom based on mvideoroomtest demo code.
I use janus module with webpack by Using janus.js as JavaScript module.
-package.json
{
“dependencies”: {
“janus-gateway”: “git://github.com/meetecho/janus-gateway.git”
}
}
So i truse janus version is recent.
iceserver is used as google stun server by setting nothing value.
Janus server is installed on digital ocean Ubuntu 20.04 droplet by following manual.
All are working.
I can see others’ video+audio stream and others can see mine too.
But streaming is VERY OFTEN not connected.
on Console, “ICE state changed to disconnected” by icestate callback,
Sometimes it works well.
Is this iceserver problem?
I tried to use my stun server by installing coturn.
But same. Sometimes works and sometimes icestate is disconnected.
Can anyone help me?
Best Regards.