Thanks so much, I'm really happy to hear you enjoyed the game! :D
As for the CG appearing again in NG+ — that's actually not a bug. It's intentional, so players who missed some scenes can get another chance to complete their CG collection.
Viewing post in New Game+ and Linux Support! [v1.7.0] comments
I might explained it too little. I did the condition for the last cg of the girls (but it not occured yet) then I start the ng+ and then when it day 2 of the ng+ the last cg of the girl occured and you can't play the ng+ because it would send you back to the main menu that what happen.
Also mc sister disappear when you start the ng+. It not really critical because you still return to main menu and come back to the save and mc sister would reappear though.