When I attempt to use the phone I haven't used for a bit, I am sometimes unable to unlock it because it seems to be processing touch events (a very long series of them) even though I am not touching the screen at the moment. It usually ends up in it being locked due to too many wrong unlock attempts, and I end up force-rebooting it.
Since it's locked, I can't even get to adb shell. It still registers actual touch events, just interleaved with these ghost touches, and one time I managed to unlock it, but couldn't do any more debugging because I wasn't near the computer at the time. It also made it worse because now it was doing random touches in my applications, initiating calls and such.
I can reproduce this most easily if I carry the phone in my trouser pocket for a while, though I don't always get it. I suspect hardware still detects the phone rubbing against my inner trousers as touch events, and I suspect the lock button is pressed accidentally.
This has been happening for a long while with my MX4 Ubuntu edition, and I am on the latest OTA update.
Let me know where should I look for log files to find what has been going wrong here? Note that this happens in the lock screen, but continues on even if I manage to unlock the screen while these spurious touches continue to happen, so it might be even lower level than unity8.
It's unlikely that unity8's at fault, we'll have to triage it to the appropriate place.