Totals not counted in overall while using SUM

We utilize Excel for our schedule and OT, and currently we're experiencing a situation where an employee is manipulating the OT, we can see the changes made in the "changes" section but can't figure out exactly the process in which they are doing to make these hours not count in the overall total. And this brings me to the wonderful minds of Reddit.

We have a column labeled "OT", and the formula in this column is =SUM(N16:NN16) for this specific employee. This counts off of their OT hours for the entire year (1/1/26-12/31/26). We've began to notice discrepancies on their OT total hours. While the formula was displaying correctly in the OT field, the actual hours didn't add up. For June 5th and June 6th we noticed their hours didn't add up. On the changes section we noticed this employee remove both hours together, readd them, remove them, then readd individually and suddenly they don't count in the overall total of the OT hours. How is it possible they aren't counted since they were readded to the same fields they were removed from and were counted prior? Is there any thing that can be done specifically not to have those counted in the overall?

There's more than enough in the changes log to more than suggest they're manipulating the OT hours, but we need to prove how they're doing it.