This phenomenon is obviously not limited to Stack Exchange, but can also happen to some professors (and teaching assistants) answering students' questions (or salesmen answering clients', or volunteers helping people in a workshop, as you describe).
I am not aware of any formal study of the phenomenon, and I would not expect one to exist (but I might be surprised!) as I think it is quite simple to explain: helpers who fail to connect with the people they help (not necessarily because they are "bad" helpers: connecting can take more energy than reasonable when helping a large volume of people in less than ideal conditions) will unconsciously feel that they help the same person over and over, and get frustrated.
The solution is to connect more deeply with each person helped (even if it means helping less people, under better conditions), and to celebrate each success as distinct of all the previous ones.
Among academic professors, there is a running joke which, I think, puts light on the phenomenon you describe:
I have been explaining this for 20 years, and the students STILL do not understand it and commit the same mistakes again and again!
This is a joke in the sense that, even though the students change every semester, a (mediocre?) professor teaching the same material again and again without connecting personally with the students gets the (irrational) feeling to be teaching the same (group of) person(s) again and again, and gets frustrated.
The solution to such feeling, of course, is to connect with each student, customer or stack exchange user rather than to treat them as an anonymous member of an anonymous crowd. If you focus on the particular background of each individual, and try to help each of them (rather than just deciding in which category to place them in order to give them the same "pattern" answer as all others individuals in the same category), in my experience each "aha" reaction from someone who was enlightened by your answer becomes a victory shining on your day/week/month. Failing to connect with individuals, you are dealing with an infinite flow of indistinct "dummies" and will ineluctably feel frustrated.
I have been teaching in various universities since 2002. I tried to think about references to justify my answer, to not much avail. I do hope that this answer, based on my experience both as a student and as a professor, will be of help to you, and that you will find back the pleasure to help fellow human beings, on Stack Exchange and everywhere else!