Hi Ruiyang,

Ruiyang Wu <ruiyangwu@math.arizona.edu> writes:

> The problem can be reproduced with the `test.tex' file attached below. When
> I tried to add more characters to the `align' environment in `test.tex',
> the syntax highlighting becomes extremely unstable, switching between math
> and plain text highlighting.

I can't reproduce what you describe.  Your file looks like this for me
where adding additional characters is no problem: