Don't send status diffferent from opened or closed because it will be an undfined satus for clients retrieving the stored message from the server.

src/main.cpp

@@ -253,7 +253,7 @@ void setup(void) {
     server.sendHeader("Connection", "close");
     boolean isOpen=digitalRead(buttonPin)==HIGH;
     server.send(200, "application/json", "{ \"isOpen\": " + String(isOpen?"true":"false") + "  }");
-    send_mqtt("statusquery");
+    //send_mqtt("statusquery");
   });
 
   server.on("/sendmqtt", HTTP_GET, []() {
@@ -300,7 +300,7 @@ void loop(void) {
 
   if (!mqttClient.connected()) {
     reconnect();
-    send_mqtt("(re)connected");
+    // send_mqtt("(re)connected");
   }
   mqttClient.loop();