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Can you check if the same occurs in safe mode?
/t5/FAQ/How-to-boot-your-phone-into-safe-mode/m-p/348008#U348008
Android doesn't suppor that, I don't know if you are aware that that's one of the top request for Android M. Samsung Galaxy Note has this feature but that's an add on
Regarding the alarm clock - it happens quite often on my wifes Z1 Compact that when it start ringing it doesn't react on touching the on screen controls. All you have to do is to turn the screen off using power button and turn the screen on again. Now it should allow you to put it into sleep or turn off.
It happened on 4.4.4, it happens on 5.0.2. I'd say that it happens for about 5 - 10% of wake ups (or I'm so sleepy, but I remember it was happening on Z1 too).