I'm running an app on the viviactive (3.10 FW) that runs fine (in fact, first time I saw this I had been running it for 6 hours straight)
On my cell phone (Andriod, with GCM 2.12), I went into devices>va>User settings, then backed out. GCM said it was "saving" (though nothing changed), and the va jumped to the first data screen of the default walking app, and froze up. I was able to do a simple power off/power up to recover, and there was nothing in any log files.
It was a bit of a bummer as I was testing how long it would run with a full charge on the va - after 6 hours I still had 42% of the battery!
update: Saw there was an update for GCM to 2.13, so installed that. user settings didn't cause the problem but devices settings did (it could be that both have the potential to do this), and this time it crashed hard, and required a full reset.
here's the err_log.txt:
1907 (vívoactive) SW ver: 310
Build Type: RELEASE
ESN: 3900590391
Battery Voltage: 3.881000V
07/22/15 22:13:43
AP
LVD
POR