Why are the square root symbols on this post different? Some of them have vertical bar and other ones have slanted bars.
That is MathJax rendering not TeX so not really on topic for this site however you would see similar from a TeX rendering.
TeX fonts have a small fixed set of square root signs (typically with slanted left bar) but then once the term reaches a certain size, TeX switches to a use a glyph for the lower part and then repeats as many "extension pieces" of a small vertical segment as needed. This last mode necessarily has a vertical left side.