@wolerdbon Hi!
So, when you connect GUI-O app (client) to the ESP32 (server) a persistent connection is established. If the server closes the client connection, client will detect this and show an error. If autoconnect is enabled client will try to reconnect every 5 seconds...
When you just "kill" the server, the client is not disconnected properly and no "goodbye" message is sent. That is why nothing happens on the client side (there are ways to handle this, e.g., keep-alive as MQTT uses for example, but this is currently not implemented in Ethernet connection.
If you try the GUI-O design tool (and exit when the connection is established), you will notice that the client (GUI-O app) reacts immediately, because when the tool closes it implicitly disconnects the client.
I can suggest you use "home" button. So, when you reboot the ESP32, swipe GUI-O from the left side of the screen to the right to open the settings menu. Press the "home" button in the upper right corner.
Hope this helps.
Best regards,
Klemen