Comment 7 for bug 1516696

@Kugi no work has been done for this as it has not been reproduced

From the unity8 log the only thing that looks suspect is a number of reports like
qtmir.surfaces: MirSurfaceItem::dropPendingBuffer() surface = qtmir::MirSurface(0x1411348) buffer dropped. 0 left.

Were you playing a lot of music perhaps in the background before this occurs?
Were you testing the app you were developing at the time?
Can you enable crash reporting and then check in /var/crash if it recurs
Also please grab the logs from /var/log/lightdm