C#/.NET Developer for Existing App

United States only We have an existing internal application that our team uses to manage service orders, labor, parts, and billing. There is one issue we have been unable to pin down and I would like to start with that before discussing any larger work. When a service order has already been completed and someone goes back in to make a change, usually to update labor time or add/remove a part, we occasionally end up with duplicate line items on the order. The strange part is that it does not happen every time. For example: A service order may have: 2.5 hours of labor Part A x 1 Part B x 2 Someone opens the order again, changes the labor from 2.5 to 3 hours, and saves it. Most of the time this works correctly. But in some cases, after the save, one or more of the existing part records are inserted again instead of being updated or left alone. The order then shows duplicate parts and the total amount is wrong. We have also seen a smaller version of the same issue where the screen looks correct immediately after saving, but after refreshing the page the duplicate record appears. We need someone who can trace what is actually happening rather than putting a temporary check around the symptom. For the first task, I would like you to: reproduce the issue if possible trace the save/update flow determine whether the duplicate is being created by the application logic, API request, or database operation explain the cause fix it without changing unrelated parts of the application I would like to begin with a paid 1–2 hour test. For the test, I will give you access to the relevant part of the project and show you the workflow where we are seeing the problem. I am not expecting you to redesign anything during the test. I mainly want to see how you approach an existing codebase, how you debug the issue, and whether you can get to the actual cause. If the first task goes well, there are several other issues and improvements in the same application that I would like help with. When applying, please tell me about a similar situation where an existing application was creating incorrect or duplicate database records and how you tracked down the cause.