Formula plugins often gets stuck

Currently the plugin has poor fault tolerance when editing formulas in latex format. There are various scenarios like:

1. enter two $$, return, then enter $$
2. Go back to the end of the first line and enter ---stuck

You can type in latex formula from this site and copy it to answer's formula and edit it a few times, it often gets stuck!

report some bug for plugin formula v1.2.9：

1. The formula of block mode（$$） is not displayed in the view view, edit preview is basically normal
2. Formulas for block mode, line breaks (\ 3 times or \ 2 times ?) or alignment (&) of multiple lines are sometimes problematic

$$
f(n) =
\begin{cases}
n/2, & \text{if }n\text{ is even}  \\\
3n+1, & \text{if }n\text{ is odd}
\end{cases}
$$