Whatsapp and YouTube are hanging on iPhone 5 16GB

I have notice that since I have upgrade iOS 7 to iOS 8, I have seen some bugs in (whatsapp and youtube) only

for example, if I'm using whatsapp and scrolling up to old conversations it gets hang without any responds so I have to press home button and remove it

I tried to restore my iPhone as new and download all the application again from applestore but nothing happy (same as before)

for youtube, it was hanging but since I have restore it , it's working ok

So anyone have similar issue specially with these two apps

Thansk

Abdullah