Second that. I bought three Nexus 5x for me and my family. Two of those bricked themselves without warning.

Plus I keep reading these stories over and over again. Multiple anecdotes in the discussion to this article alone...

Both got repaired (mainboard replaced) under warranty without issue. I'm still happy with the phone and haven't found anything comparable considering the price (270€ approx. 1 year after release), but you definitely need to have a solid backup strategy.