The "From Workspace" block in Simulink expects data in a timeseries format, where the first column is treated as timestamps. This is likely why the first number in your matrix is not appearing in the sum, as it is being interpreted as a timestamp rather than a data value. For more information, you can refer to the documentation for "From Workspace" block: https://www.mathworks.com/help/simulink/slref/fromworkspace.html
To resolve this, use the "Constant" block (https://www.mathworks.com/help/simulink/slref/constant.html) instead, which allows you to input your matrices directly as data without any time-based interpretation.
