What colour are the LEDs on the top of your OPTA ?
It looks like the board is not responding to the messages from the agent and the port got closed.
What happens if from this state you stop the web procedure, open a serial monitor and reset the board ? You should see something like this:
Starting Provisioning version 0.3.0
BLE Available
Waiting Ethernet configuration from DHCP server, check cable connection
timeout: 250, response timeout: 500
…
NetworkConfigurator: Connection fail: Failed to connect
At this point the LED is blinking blue.
Are you using ethernet or WiFi?