Congratulations! you've reached one of the most annoying bugs in Power BI.
You can read all about this in here: https://www.sqlbi.com/articles/why-power-bi-totals-might-seem-inaccurate/
Or here:
https://community.fabric.microsoft.com/t5/Desktop/Measure-Total-Incorrect/td-p/3013876
In my case, the "best fit" solution is to export to CSV to make sure the numbers are correct, but there are other options. Sorry about that :(