I have a Samsung S5 running Android version 6.0.1. I've had it for a couple of years, and it has just started freezing on me in the last 3 weeks.
The problem seems to occur if I turn the screen off while I'm in WhatsApp with the keyboard displayed. When I next turn it on, instead of seeing the lock screen, it shows the keyboard. The phone doesn't respond to any keys so I have to power off completely. Luckily, I can do that without having to remove the battery.
Has anyone else seen this problem with WhatsApp on Android?