@ThomasAH: If his device is rebooting because of the kernel change, "load default" is what's happening already on boot, and will fix nothing. If it's not because of the kernel change, load default will still do nothing, since again, that's what the system does at boot, unless the system is rebooting more than once within a smaller (5 minute?) window. Specifying the standard kernel with lower CPU ranges on command line (as shown above) will fix it, if it's the kernel (which I doubt).

It's more likely that something you have setup to run every hour or so is causing this. A widget or some other thing you recently installed/updated that's trying to do something every hour, and on failing it's locking the desktop, and eventually causing the watchdog to reboot the system.

My first bet would be to turn off all your widgets and see if you stay up for more than an hour. If so, add them a few at a time to see which one is causing the problem.