The matrix was found on this paper: https://www.hrpub.org/download/20190830/UJER21-19513535.pdf
The answer is
If you look at the three symbols in any row or column, and only look at either the horizontal or the vertical lines of the symbols, you will find that one of them has one line, one has two lines, and one has three lines. Also, one uses thin lines, one uses thick curved lines, and one uses outlines/rectangles.
The only symbol that completes that pattern for both the horizontal and the vertical lines is #5.