I just tried it on my Sony Xperia Z2 and I am encountering the same problem on this device…
Could it have something to do with the fact that I only have the demo version? Like first startup works fine, and it doesnt say its a demo in the far left corner.
2nd startup it says (demo) after the version number though no arrow keys or buttons.
EDIT: I found a solution for my problem at least.
Even though the D-Pad/Keys doesnt show up on the screen they are still there, just invisible. Successfuly navigated myself to the in-game options.
Options -> Control -> Touch Controls: D-Pad -> Classic D-Pad
Options -> Control -> Touch Controls: Input Buttons -> Classic Input Buttons
Then saved and exit, now when I restart the game I get both D-Pad + buttons.
Hope this help others who encounter the same problem.