The camera on my Xperia works fine on Sailfish and scans qr-codes without too much effort, just not the whatsapp-web one. It looks more like a qr-code related software issue.
For testing I took a picture of a small qr-code and displayed it on my computer screen. The camera app reads this small and badly lit qr-code with ease, from the same computer screen where the whatsapp-web qr-code is ignored.
