Take a look at this post. Quote:
It is known that Visual Studio does not sort projects alphabetically when projects are inside Solution Packs. Since I work on fairly large solutions (more than 20 projects for 1 solution), and how to order projects through Solution Packages, this is a very annoying mistake.
However, I accidentally discovered a solution to this problem. Follow the steps to sort your projects alphabetically inside the Folders solution.
Right-click the project and select rename (or just select the project, wait 1 second and click it again or press F2). Do not change the name, just select another project.
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