I've had this problem on my Z10 for months. And I have tried updates and all sorts of other recommendations from various forums. But it usually rebooted daily but while idle. But Last week it did it twice while I was using it. Yesterday it rebooted three times inside of a couple of hours. So I took it to the AT&T device service center and after their diagnosis, they were very confident that it is all due to a bad battery. (This is plausible given the fact that bad batteries have recently been known to ground airplanes; why not my cell phone.)
Anyway, AT&T is sending me a new Z10 battery I hope to report back with positive news by the end of the week. If it can last more than 48hrs without a reboot, I will let you all know. Let's keep our fingers crossed.
UPDATE (From May 5): I received and installed the new battery and charged it overnight. Unfortunately, it did not make it past the 25 hour point before freezing in my hands and rebooting.
Next up, a call to AT&T, Hopefully I'll get forwarded to BlackBerry.
PS: I have experienced the reboot several times while using a particular app. It is my most used app, so this is not unexpected. But as an experiment I have uninstalled the app and I will attempt to live without it for a few days just to see if this extends time between reboots
PPS: the reboots would not be such a PITA if Bb10 supported 'Headless" and auto started event driven apps... (like start on powerup)
Bullety, sorry but, I don't use WhatsApp. My "addiction" is reddit.com so I spend a lot of time using a viewer app. (I will bring it up with the dev if and when I can show some stronger correlation data). Random reboot happens even when this app is closed. The only apps I leave in active frames are calendar, reminder and battery guru. Battery Guru has only been used for past few weeks to help track battery usage 'signal '. This reboot **bleep** has been going on for months. I am yet to try going without any active frame apps for an extended time... that may be next. it's a real goose chase! I hope BlackBerry gets to the bottom of it asap.