I tried the app again, and it seems like there is a conflict between the swipe gestures and the drop button. I’ll fix this in a future update. Thanks for reporting!
Regarding the top letter, it shows the next letter that’ll appear after the current one has dropped. Do let me know if that’s not what happened?
The last one is a rare issue and I haven’t faced it in the latest build. That said, I’ll try to do a double check to to minimize/remove this in the next builds.
Have fun!