demo3 isn't usable after reset
If you were able to register the device, there shouldn't be any problem.
Yes, it works now, but it hadn't worked before (~10 hours ago).
We haven't touched the server.
Well, the issue may be related to Android Client - I had restarted it overnight, and after that it could send the buffered data.
It seems demo3 was reset recently, but after registering the device, Traccar Client (Android) can't send data (Send failed).
Probably the server was partially reset and something is stuck there, because the IDs for new devices don't start from 1, but continue old sequence.