I would do one of the following to try cure it.
1. Kill the app from background and relaunch it again. If it doesn't work then
2. Kill the app from background and reboot the iPhone, then launch the app. If it doesn't work, then
3. Delete the app from the iPhone and reinstall it again. If it doesn't work then
4. Write contact the programmer of the app and leave him a feedback, than wait for an update. While waiting for an update to correct the issue, you can look into some alternatives to that application.