I'm using vim 8.0.94.  In a TeX file (specifically LaTeX), the three occurrences of \(\) in\(\){\(\)}{\(\)}should be highlighted in the same way, but they are not.  Curiously, in the second, but not the third, the \( is marked as plain text, and the \) is marked as an error.  I used to be able to find my way around syntax.vim files, but the TeX one is too complicated for me to figure out what's causing this.  (I don't even know whether to look in the command section or the math-mode section.)
Fix syntax highlighting in LaTeX
syntax highlighting
You can get the name of the syntax item under the cursor with::echo synIDattr(synID(line('.'), col('.'), 1), 'name')In this case, it's apparently texBadMath.Looking at /usr/share/vim/vim80/syntax/tex.vim I see there are three syn match commands for this: Bad Math (mismatched): {{{1if !exists(g:tex_no_math) && !s:tex_no_error syn match texBadMath           \\end\s*{\s*\(array\|gathered\|bBpvV]matrix\|split\|subequations\|smallmatrix\|xxalignat\)\s*} syn match texBadMath           \\end\s*{\s*\(align\|alignat\|displaymath\|displaymath\|eqnarray\|equation\|flalign\|gather\|math\|multline\|xalignat\)\*\=\s*} syn match texBadMath           \\[\])]endifThe s:tex_no_error is set from:if exists(g:tex_no_error) && g:tex_no_error let s:tex_no_error= 1else let s:tex_no_error= 0endifAnd is documented: 5. If you have the variable g:tex_no_error defined then none of the    lexical error-checking will be done.    ie. let g:tex_no_error=1So adding this to your vimrc is the easiest option. This should result in:A more difficult route is to fix this syntax file. The line that causes this error is the last one:syn match texBadMath          \\[\])]The \s make it a bit confusing, but a literal \ followed by a ] or ) is considered an error.I'm not really familiar with TeX, but this should be comprativly easy to fix. You could contact the author of the file, which is listed at the top.