I just bought a new smartphone and the new Android (6.0.1) has this peeking thing that really annoys me. I wanted to disable it, for example for WhatsApp, so I went to
Settings -> Sound & notification -> App notifications -> Whatsapp -> Allow peeking (off)
This solves the issue. The problem is that when I turn the device off and then turn it on again, these settings go back to default and the peeking is re-enabled without my doing anything.
Is there a way to permanently disable peeking?
I've found this link and option 1 seemed very promising. However, I did that and it didn't work either. Still looking for the solution, though.