On my iPhone 6 auto update feature updated my WhatsApp to version 2.16.5 on May 31, 2016, after that moment whenever I tried to open my WhatsApp it shows a blank white screen and freezes for 4-6 seconds and returned to home screen.
after searching the internet I found a workaround to temporary fix this issue.
it is simple
Close the app via multitasking (double click home button and swipe away the whatsapp window)
Go to Settings>Whatsapp>switch off everything except cellular data and notifications
It should now respond hopefully (responded for me)
Now go to Settings>Whatsapp>and switch on everything
Open whatsapp again and it should work now.
UPDATE: WhatsApp 2.16.6 fixed this problem, on 03 Jun 2016.