I started having this happen on my Verizon Note 4 the last couple nights. I'd wake up in the middle of the night to the bright red Verizon boot screen, and nothing I try can fix it except pulling the battery.
It actually did it to me night before last, I did a battery pull and reboot it, and when I woke up again the next morning it was stuck on the boot screen again.
I've been having a lot of annoying small bugs with Lollipop, but this one I consider a deal breaker since it means I can't trust my alarm to go off anymore either.