My phone, Samsung A8 2018, sometimes vibrates without there being any notification. I've noticed this since yesterday. The two new things which yesterday changed about my phone are: I updated my phone and I started playing games through facebook. I've reset my phone's notification settings and at least one of the games does also send notifications when something happens. The other one doesn't, but I haven't noticed any correlation between the virbations and something happening in the game.
Smart Alert is turned off.
Something which might be irrelevant: permissions for certain apps (Whatsapp and Snapchat) got reset, either after the update or after resetting notification settings.
What causes these vibrations without notifications? Is there any way to check what causes a vibration?