Hi, really enjoy this, it really hits my sweet spot. I do have one small issue though, occasionally in portrait mode the touchscreen seems to get out of sync with the board, so that when I choose a tile it actually selects a point a few millimetres below, so unless I touch the very top of the tile it's often a different one.
I think the cause is either turning the display off and back on again, or possibly minimising the app and reopening it. It doesn't seem to happen at all in landscape mode.
I'm running the paid Google Play version of the app on a Google Nexus 5X with the latest Android 7.0.