I am getting the below message very often. It does not prevent the CMS to work though.
"A real-time connection could not be established with the server. This may be caused by incorrect configuration. Please see the User interface section in the user guide for further information."
This is when you are running site without debug (ctrl+f5) and you change in code. Then you will need to refresh you website(CMS). That's all about the message is.
It sounds like you didn't enable Websocket in IIS?
For that, do we need to have site hosted in IIS? Or this is applicable for any case (like running site as ctrl+f5)?
I'm not 100% sure, but I would guess it'll be the same
I just verified that it (WebSocket Protocol) is enabled for me in IIS and I am running my site using ctrl+f5. I still see that popup in CMS everytime I do a code change/build.
That's expected because when you build the site because it's basically a restart, and I would think WebSocket need to refresh/reestablish the handshake.
However if it pops up everytime as OP mentioned then you should look into enabling WebSocket