sleep of death nexus 4

I have Nexus 4 with Android 5.1. Recently it started to get Sleep of Death occasionally. I think it started after updating Android from 4.* to 5.*. I read that it's bug in Android Lollipop and some advises to fix it for example to turn off wi-fi when phone sleeps. I tried, but it didn't help. Some other advises: one , two , three . I don't know which I should follow, it required a lot of time to try them all. And I want to avoid rooting.