Sadly, this is an Apple bug that has been around since iOS 7 arrived, and is still not fixed. I’m afraid we can’t do anything about it, although you may find that turning your phone 180 degrees may help.
Here are some more details:
iOS 7 and 8 have a strange feature that interferes with touches on the bottom left corner of the iPhone screen. That means the left three white keys in the on-screen keyboard don’t work properly. To successfully play those keys, you have to move your finger slightly when you touch the key. Apple have not yet responded to a number of developer complaints, nor to our bug reports.
Posted in: Other bugs and problems