My OnePlus One phone got stuck in a boot loop over night without, as far as I know, a specific reason to do so (no new update was installed). Before this it was running perfectly fine. The phone was running the stock CM.
The phone boots and shows the Cyanogen Mod Ready logo and then restarts (Android version 6.0.1, Cyanogen version 13.1.2).
I tried numerous things so far Booting in safe mode, wiping the caches and a factory reset (as suggested on the boot loop info page) all did not solve the problem.
Using ADB sideload to push and flash a zip of the ROM from the computer did not work. Yet no error was returned.
Furthermore, flashing the ROM with fastboot, as described here: http://forum.xda-developers.com/oneplus-one/general/guides-bacon-timmaaas-how-to-guides-t2839471 did not resolve the boot loop. Also here, no errors were returned when flashing the individual files.
I'm not sure what other options I could still explore.