It's not a bug.Hey there, I downloaded version 3.1, but it seems to still have some issues I think, for me at least. Whenever I complete one of the tasks in the day, it seems like the game doesn't remember and the same task is available indefinitely. In other words, I can go for a waltz with Astrid over and over again day after day and it doesn't disappear or advance the story.
You have to increase your affinity with side girls (like Astrid) to progress further on her story. If you fail to get the affinity point with her during the Waltz event (or any other event), that event will pop-up again until you suceed.
It works a bit differently with the 3 main girls (Nox, Astrid, Candrid) whose story will progress no matter what (but it's obviously recommended to try to get the affinity points).
I believe there is a PDF guide/walkthrough on the OP in case you are a bit lost