Please be wary when you see a flashing message from WhatApp that it needs to install an Update today. It has been doing these so-called Updates ala Windows10 and frequent basis of late.Previous Updates have not created any problems.The latest one,today, after trying to install the Update,flags up that the entire WhatsApp app needs reinstalling. Opting for that inevitably wipes out any previous messages,etc and you have to re-start all over from the beginning.
