Kindle not responsive to touch on ipad mini

When I finish a book, I normally tap the upper left hand corner of the screen to get back to the my Kindle home screen/library. Lately, it has become unresponsive, and it appears to be random. I've tried re-starting, uninstalling and re-installing Kindle, and making sure updates are current. This only seems to happen with my Kindle App. Does anyone have any insights? Thanks in advance.