This issue is back again since around Nov 2019, and persisting as of today, Oct 21, 2020. Almost a year with no solution.

What is happening is that device registrations are being expired by the Voipo servers about 20 to 30 seconds early.

Example, if your device registers for 300 seconds (5 minutes), then Voipo will expire the registration at about the 230 second (4.5 minute) mark. So your inbound calls will fail for those final 20 or 30 seconds.

You can try setting your device to remain registered longer, but 900 seconds (15 minutes) is about the maximum you can get away with, since most routers will close the UDP ports every 15 minutes. You need to keep registering to prevent this.

At 900 seconds, that is 3.3% failure rate. So 3 out of every 100 inbound calls will fail. Of course, if your device is set to 5 minutes, you'll get 10% failure. And for PBX users, the default registration of 2 minutes will result in a 25% failure rate. None of those rates are acceptable.

I've had numerous tickets open with Voipo, including direct emails to Tim the owner. However, there seems to be no progress, despite the critical nature of this issue. I only get an occassional response that their developer team is aware of it, and working on it.

If you want to duplicate the issue, just set your device registration expiration to something fairly short, like 120 seconds (2 minutes). Then log into your voipo control panel to view the device registration. Refresh the page periodically, especially as you get close to the last 30 seconds. You'll see your device disappear for 20 to 30 seconds. Then at the correct registration time, your device will register and appear again.

Anyway, just feel like I need to post this, since Voipo doesn't mention it on their Twitter issue notification page.