That's not bug nor android issue, that's your lack of knowledge - you would know about it if you read the changelog - dev intentionally locked relationship progress on levels 20 and 40 (60 and 80 will come later) behind certain special interactions with Yuna.
If you want the standard and intended way, before the night starts choose option to give gift to Yuna and then "chat" with her (dont ask me why it's there, not my choice) she will give you a hint about what you need to do in order to progress
If you want the short way - read changelog for 0.3.4 (or search the page for " 20" and " 40" [include whitespace in front] to find the entries you want)
Cheers