Thx @Mykle1, indeed I have. See the beginning of my (working) config file below.
What is suspicious to me is that not even a Ping works to that IP, even though I’ve checked it by printing it on the screen of the MM and in the router.
Also, before my Whitelist was a long list of IPs, now I’ve tried the [] option but to no avail…
/*************** AUTO GENERATED BY REMOTE CONTROL MODULE ***************/
var config =
{
        address: "0.0.0.0",
        electronOptions: {
        },
        ipWhitelist: [
        ],
        modules: [
                {
                        module: "alert",
                        config: {
                        }
                },
                {
                        module: "updatenotification",
                        position: "top_bar",
                        config: {
                        }
                },
                {
                        module: "MMM-Remote-Control",
                        position: "middle_center",
                        config: {
                        }
                },