I'm not sure if this is useful, but I remember that in the August version of the game, when the scene was about helping Nao escape her cell, the bug happened as well after using lockpicks on the door. Back then, I thought it was because the scene was not updated yet.
Perhaps it is about using lockpicks in-between dialogues, or maybe the floor of the tower or the configuration of the dialogue have the curse, then again, I don't know how these things work.
----
The guards of the "floor" thing are in the southern exit of Tolbana.