If you're running on a Unix-based system, you should have a file called
~/.vim/syntax/tex.vim. (I do not know where to find it on Windows). You can find the math-mode syntax configuration in the
Math Zones sections. According to your screenshot the other math environments do not have the same issue. You may be able to fix that by looking for a working environment such as
displaymath for example and add similar entries for align.
Another more brutal method is to disable the error highlighting for TeX files. It can be done by adding the following in your
Here the documentation provided by
Tex: Excessive Error Highlighting? ~
The <tex.vim> supports lexical error checking of various sorts. Thus,
although the error checking is ofttimes very useful, it can indicate
errors where none actually are. If this proves to be a problem for you,
you may put in your <.vimrc> the following statement: >
and all error checking by <syntax/tex.vim> will be suppressed.