I have the same problem since a long time. I use ESP8266 alone, without an arduino, latest app/library and Android 4.4.2 smartphone.
Everything works fine for a random amount of time (from less than an hour to more than a week), then, if connected, the RemoteXY App will return to main screen. And trying to reconnect will show the error. The only way to reconnect again is to reset the board. But when this problem happen, the rest of the program on the ESP is still running normally, as confirmed by a webserver still responding to requests, NTP request working, Serial commands responding, etc. It's just the RemoteXY connection that seem to be broken.
I will add more infos if I find something, maybe I can find a way to reproduce the problem easily, this would help track the problem and solve it...
Actually I am testing the Cloud feature with an ESP32 since two days, with a minimal sketch (just show the value of millis() in a Text element, every 5 seconds) and it disconnected only once. But when it was disconnected, the only way to reconnect was to press the reset button on the ESP32 devboard. So it seem to be the same problem.
It is probably related to WiFi..!