Which character's quest is this? The rules and the quest logs aren't connected so I suspect there's something else going on.
I forgot the name, but it was the lesbian girl that have interest with the PE teacher, the questline was empty but Rachel(?) questline is still there. probably there is other character as well (i guess the arrogant girl who want to marry rich dude?) but it was only on the student quest that have this problem (the main and teacher quest is okay). Also i just notice that the game work normally (i can interact with the girls just fine), but i can't see the progress of the some student in the quest menu as the quest is disappear for those character.