Some users have reported distorted or missing buttons in some of the dialogs in the app.
Problems with dialog layout are often caused by a change to the default system font size. In the System Settings look under Accessibility > Vision > Font and Screen Zoom, or something similar. The screen zoom and font size should be set to normal.
If you are using a very small phone (eg 3" screen), it may help to use the app in landscape mode. Use the back button the exit the app, rotate the phone and launch Memory-Map while the phone is rotated.