It happened to me months ago. And it happened also few times, also early morning hours.
In fact I was answering the call, there wasn't anyone calling, hang up, and few secs/minutes later
it will ring again. The only way to stop this pattern was literally to reboot the obi in the middle of the night.
It's been long time so I don't recall what was in the call history. I havent' experienced it though
for several months.
L.