Every now and then, I'm producing a single and say I want to get the choreo made, if I drag it to the choreographer it won't let me? I can drag it to her, the icon'll disappear but nothing happens. Similarly, dragging idols would ocassionally not drop onto the room but sometimes the icon of the girl remains. It stays like that until I somehow manage to drag her or another idol successfully or reload the save. Sometimes, usually for the marketing of a single, it won't let me click on the single to drag to the staff. I end up having to cancel it and redo it since restarting doesn't fix it (as far as I'm aware).
Edit: I actually managed to fix this issue (editing the save file wherein if girls wasn't -1, change that to -1 and status to 0). Without fixing it, apparently the staff members weren't assigned to a room but time still stopped.