Least favourite plot device used in too many stories you otherwise enjoyed
Independent Harry stories are amongst my favourite Harry Potter fan-fiction tropes. Unfortunately, despite my enjoyment of this type of story, there is one plot device that is often employed within them that I find a little irritating. That is the inclusion of a room or, in some cases, trunk with some kind of time distortion allowing Harry and, occasionally, his friends to complete years of training in a matter of months, or even weeks. This is definitely my least favourite plot device utilised in stories I otherwise enjoyed.