When i opened my Whatsapp in my Android phone (Samsung phone), i could not scan QR Code to link my computer to my Whatsapp.
The camera when scanning QR Code couldn’t focus, so the QR Code in my computer looked very blurry.
However the camera works fine outside Whatsapp (for example on built-in Camera apps).
So the cause was the “Scan QR codes” (under intelligent features) in the camera setting was turned on.
When i turned it off, scanning QR Code within Whatsapp application works fine and the camera can focus.
Also you can try to clear cache of the Camera apps, and the cache of messaging (Whatsapp / other).