All we can tell from the symptom you describe, is that the OBiTALK portal is warning you that it cannot contact your device. This doesn't mean that whatever Internet Telephone Service Provider you're using is going offline or not working. If you have done anything to customize the system management parameters on the OBi device, such as disabling connection to the OBiTALK server, then that would explain it.
There are too many other possibilities, to be able to definitively point to one cause. Typically, in a properly working setup, you would not receive this message unless your internet service went down for more than a few minutes. So, you may have unreliable internet service, or you could have an issue with the LAN equipment and cabling going to the device, or it could be a bad power connection. Next time you receive the notice, immediately look at the device, to see if the LEDs are on. The middle LED should be periodically blinking. If it isn't, the device has a problem reaching your network. If it is blinking, pick up the phone and attempt to call **9 222 222 222 and listen for the "Welcome to OBiTALK..." message. If you don't hear it, the device lost connection to the OBiTALK service.