I am using Chrome or Firefox to send commands to the Teltonika router
Router which is connected to the lan with ethernet cable, to the same switch to which the pc used to send the commands is also connected
And therefore, apart from the ethernet switch, there is nothing between the computer and the router that can go to sleep and prevent the connection
But in your case, if you use a web browser to send the command, after how many seconds do you get the OK response in the browser window?
Command on web browser address bar, like this
Same thing even if the router has not been used for more than 10 minutes or does it change?