Total hang of krillin - mali_timeline_sync_fence_create() fail

I've had total hangs with both OTA-5 and now OTA-6 on my krillin. This was the first time I had developer mode enabled when it happened. With total hang, I mean no interaction is possible besides turning screen on/off, and the hang does not go "by" ie it's not apport running. Auto-dimming is also still functional during the hang, as is brightening the screen when touched.

However, I was not able to adb in in this state (I kept the screen on throughout until I was able to try adb):
$ adb shell
error: protocol fault (no status)

$ adb devices
List of devices attached
JU012772 device

$ adb shell
error: closed

The fault/closed statuses did take a minute or so to arrive, unlike when the device is locked when the "closed" is immediate.

Hang happened at 12:48 (clock stalled at that point). Forced reboot at 13:01. No .crash files generated. The log files below were touched at 12:47 or later. I browsed through all of those and mostly nothing extraordinary was seen. Only two with timestamped logs showed any activity during the hang, but indeed they did show it was not total hang even though also adb was not working. Those without timestamps are hard to know when the messages were logged - before the hang, during the hang or after the reboot.

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2194 Sep 11 12:48 application-legacy-webbrowser-app-.log.1.gz
 130 Sep 11 13:01 indicator-network.log.1.gz
  91 Sep 11 13:01 untrusted-helper-type-end-push-helper.log.1.gz
 117 Sep 11 13:01 application-failed.log.1.gz
 457 Sep 11 13:02 usensord.log.1.gz
  41 Sep 11 13:02 ofono-setup.log.1.gz
1673 Sep 11 13:02 mediascanner-2.0.log.1.gz
 118 Sep 11 13:02 telephony-service-indicator.log.1.gz
  57 Sep 11 13:02 click-user-hooks.log.1.gz
  94 Sep 11 13:02 tone-generator.log.1.gz
 178 Sep 11 13:02 indicator-messages.log.1.gz
 228 Sep 11 13:02 pulseaudio-trust-stored.log.1.gz
  52 Sep 11 13:02 cameraservice-trust-stored.log.1.gz
 113 Sep 11 13:02 mtp-server.log.1.gz
7691 Sep 11 13:02 account-polld.log.1.gz
 272 Sep 11 13:02 ubuntu-location-service-trust-stored.log.1.gz
3916 Sep 11 13:02 ciborium.log.1.gz
 465 Sep 11 13:02 maliit-server.log.1.gz
 323 Sep 11 13:02 nuntium.log.1.gz
 935 Sep 11 13:02 media-hub.log.1.gz
 370 Sep 11 13:02 address-book-service.log.1.gz
 195 Sep 11 13:02 ubuntu-push-client.log.1.gz
 257 Sep 11 13:02 sync-monitor.log.1.gz
 624 Sep 11 13:03 unity8-dash.log.1.gz
2001 Sep 11 13:03 scope-registry.log.1.gz
3018 Sep 11 13:03 dbus.log.1.gz
8870 Sep 11 13:03 unity8.log.1.gz
 885 Sep 11 13:03 application-click-com.ubuntu.telegram_telegram_1.3.20.114.log.1.gz
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The attached image shows how the phone hanged during starting Telegram. The poor picture quality is from the laptop's webcam, since I was on lunch when the hang happened. Note that the ghosting of two different sized "Telegram" titles is not an optical illusion - there were two overlapping texts with different sizes. That is, it was transitioning from the splash screen to the smaller title with a logo. The previous hangs have happened eg similarly when launching an app, or swiping the multi-tasking view, ie when device is under active use, never during idling.

account-pold was clearly during the total hang. Also ubuntu-push-client had one line: 2015/09/11 12:51:06.632108 INFO connectivity check passed.

pulseaudio-trust-stored.log had a non-timestamped lines with (this it the whole content of the file):
Attempted to unregister path (path[0] = core path[1] = trust) which isn't registered
reattempt connection to mir...
reattempt connection to mir...
reattempt connection to mir...
reattempt connection to mir...
Error during initialization and startup: Dynamic exception type: N4core5trust3mir20InvalidMirConnectionE
std::exception::what: Cannot create instance for invalid connection to Mir.

cameraservice-trust-stored.log.1.gz also had the single line:
reattempt connection to mir...

I've saved the potentially interesting logs for account-polld, dbus, unity8 and telegram for later watching. No other log files seemed to have anything of interest.