As you've discovered, everyone has a slightly different suggestion. I found this really confusing when I did my MSc thesis. As I wrote more of my thesis, my supervisors kept tweaking the structure. The changes they made were definitely for the better, and I was satisfied with the end result. But I felt like I should have (somehow) known the right structure to use.
Folk might have their own opinions on their favourite wording of the following sections, but here is a basic outline of the structure of a significant technical work, such as a thesis.
Thesis Structure | UNSW Current Students
Suppose you are taking a course on 19th-century America, and the instructor hands out the following essay assignment: Compare and contrast the reasons why the North and South fought the Civil War. You turn on the computer and type out the following:
The easy answer is 'yes and no'.
There are certain conventions specific to certain disciplines. However, these structures are not imposed on a piece of work. There are logical reasons why there is a conventional way of structuring the thesis, which is after all the account of what you've achieved through your research. Research is of course not conducted in the step-by-step way this structure suggests, but it gives the reader the most accessible way of seeing why this research was done, how it was done and, most importantly, what has been achieved. If you put side by side all the questions you had to answer to finish your research and what is often proposed as a typical structure of a thesis, then you see the logic of the arrangement. That does not mean, however, that you have to name your chapters in this way. In some disciplines, it very often is like this; in others, this structure is implied. For example, in many science theses, the following basically is the structure; in many humanities theses, the final structure looks very different, although all of these questions are answered one way or another.
Your thesis is a long and complex piece of writing, and in order to do justice to your research findings and their significance, it is important to communicate clearly and effectively. You must provide as much helpful structure as possible to guide the the examiner and readers by linking sections of your writing and indicating the structure of the chapters and sections wherever appropriate.