Thanks for the message.
I’m using the standard dialer (com.android.dialer). I’ve also experienced similar frozen screens in some apps, specifically I remember it happening while using the WhatsApp and Wikipedia apps (maybe once/twice a week?). Sometimes I’ll be scrolling through something and the screen will start to stutter, with the left half of the screen lagging behind by a fraction of a second. Most of the time it’s fine, but sometimes the phone will freeze. Next time I have another camera to hand I’ll take a literal screenshot 
.
I suppose it could be a memory issue. I’ve checked the memory in the developer options and it seems to read 1.1-1.2 GB used. I’ll keep an eye on that next time it happens.
What app can I use to keep an eye on CPU usage?