I’ve had the similar problem on an old tablet running a custom ROM. I believe this was caused by either a kernel bug or some other low-level performance bottleneck in the filesystem. None if the user accessible stats showed why the tablet was constantly running hot and slow as hell. The only fix I’ve found was a factory reset. I don’t know what got corrupted, but I found debugging not to be worth it.
My guess is that a system component has a bug and is in some sort of a crash/retry loop.
Another thing you can try, that I just thought of, is to look in the battery stats and look for wake locks. Applications can tell the OS not to go into deep sleep (for instance, a media player may want to keep running after you turn off the screen) and sometimes buggy apps can keep their wakelocks unintentionally. Dumping the wakelocks may help figure out if an app is keeping the device awake for no reason