Vortex lost its connectivity to Android application

I have got pack of two Vortexes. They both worked with VortexBot for Android properly. Yes, that application was quite often incidentally terminated but I could dfrobot with it. However, primarily I wanted to test programming of the robots. There were some obstacles on the way, manageable with help of DFRobot experts (thank you, Rex:). Eventually I can control my robots from Scratch scripts running in PC with full functionality described in S4V tutorial, using both possible connection options: usb cable or Bluno bluetooth. I have also successfully tested Scratch for Arduino according to instructions in DF4Scratch Manual, as well as Arduino IDE. It is more difficult to get practical results using these tools because of missing Vortex documentation, but that’s another question.

Unfortunately somewhere on my way to this point one my Vortex lost its connectivity to the Android app. Having two robots I can compare them, anyway, after more comparative tests I have to give it up and would need a help again.

My observations (the handicapped Vortex is referred below as B - bad, the right one as A):

1. The Bluetooth module in Vortex B should be ok because it can connect and communicate via Bluno adapter to node.exe in PC.

2. The mobile app should be ok because it connects and communicates to Vortex A. Android also for sure sees the Vortex B (so the app should see it as well), because the Android Bluetooth Settings indicates ’Vortex (C914)’ as available device. The device also enables pairing with PIN but that is probably useless in this case. The Vortex A is reported as ’Vortex (C140)’ there.

3. I have been told by Rex, that “The mobile app will prompt for firmware upgrade when the code in Vortex is not the latest official firmware. Does not matter if you put firmata, blink or older version of firmware on it, it will prompt for upgrade. Detection process is protocol based.” So the content of flash memory doesn’t matter. I can confirm this, having done tests with the standard firmware, Firmata and even a void sketch produced by Arduino IDE. The mobile app never gets any connection at all.

4. Hints given in Common usage FAQ (switch the Vortex off/on, stop/start comms service) do not help.

My considerations:

5. I watched in the node.exe log that the Vortex appears to PC identically, whether it is connected by cable or via bluetooth. The PC probably never knows which option is just being used. The Android app should initiate the connection similarly, after all, on Vortex B side the detection process is “protocol based”, i.e. it must be supported by some small routine within the bootloader. One can hardly believe the bootloader could be accidentally damaged.

6. I also doubt that EEPROM memory could be important. I have listed the EEPROM B content, which, of course, says me nothing. I did not compare it with A because to get A listing would require uploading a suitable Arduino IDE sketch to Vortex A and I don’t want to overwrite its standard firmware, which is still the original installed by DFRobot. In fact I did all experiments comprising such overwriting with Vortex B only (this is the only difference between both robots history known to me), so I am afraid of losing A connectivity as well.