Supervising same work again and again
This is a poor supervisory practice. Unfortunately, it becomes increasingly common in Universities, particularly in countries with strong marketalization of Higher Education (e.g. US, UK). Students are treated as customers, and academics are assessed and promoted based on their &quot;efficiency&quot; in terms of the number of students they supervise, not the quality of education they provide. The pressure on academics to supervise more students is constantly increasing, and they rarely have enough time to meaningfully prepare to supervisory meetings. It is not surprising that many academics find it convenient to reuse the same projects over and over again.
UPD: Answering comments, I want to clarify why this practice is detrimental to students' learning. Project-based learning attempts to recreate an authentic experience of doing something, then encourages students to reflect on this experience and learn from it. The authenticity of experience is the key for success. However, after some repetitions the supervisor knows all good and bad ways around the project, and unconsciously projects them to the student. Students don't have the same feeling of terra incognita in their research. Of course, realistically, we can't expect each master project to be completely new, but it's still important that the supervisor has not rehearsed it by heart yet.
A closely related, but not exactly the same reason is potential plagiarism. All theses are published and could be dug out by students. I have seen some supervisors who passed good theses from past years to new students to &quot;get the style&quot;, effectively encouraging plagiarism. But they had way to many students to supervise and no time to do it properly. Surely, copying from someone else's paper is a poorer learning experience for students compared to doing research themselves.