having recently removed my Cortana live tile from my lumia 640 lte my phone response time has improved quite considerably. the problem started with WhatsApp. it was always 'resuming' whenever I opened it and could find out why it was so slow at responding, so much so, I did a factory reset then reinstalled WhatsApp with the 'resuming' issue still in place. it was a chance read on a post somewhere on a forum I've since forgotten that I read a remark that said something like 'some people think its the Cortana live tile...' I then proceeded to unpin the tile and hey presto my phone began to run normally again and respond quickly when I opened the WhatsApp tile. since removing the Cortana live tile I've had no more issues with 'resuming' and the phone responds quickly like it used to. turns out I didn't need to do a hard reset after all - just unpin the Cortana live tile. if any one else has experienced this issue please post here with what's happened and pass it on. cheers drew.