WebGL build with SocketIO throws errors

When I built WebGL with SocketIO, I got some error with that.
Sometime I can connect on SocketIO. When I try to refresh web brower, I cannot connect with below error
Please help me out.

FM WebSocket may fit your need. or you can write your own js wrapper for socket.io.

asset store: FM WebSocket 1.0 | Network | Unity Asset Store

It supports WebGL Build.