my screen locks it self and won't respond to anything (nexus 5x)

[AC Question]

my nexus 5x has been a dream so far but today something weird has happened it just turns the screen off and wont respond to anything i do when i reboot the device it stays normal for like 3 mins then shuts off and the only thing that seems to work is the safe mode so what is the problem and i got the system UI not working only once