Katex shows abnormal display

[ZhihengNing]

I have a Latex code like
$\boldsymbol {x}i \in \mathbb{R}^p, \boldsymbol{u} \in \mathbb{R}^p,\boldsymbol{\Sigma} \in \mathcal {S} {+}^p $
It can display normally when I replace it with Katex code:
\(\boldsymbol {x}i \in \mathbb{R}^p, \boldsymbol{u} \in \mathbb{R}^p,\boldsymbol{\Sigma} \in \mathcal {S} {+}^p \）
But it cannot be displayed normally, why? (By the way, I hope to add support for Latex #1789 )

[ZhihengNing]

The mathematical formula is rendered correctly locally

but the following problem occurs when it is rendered on the github page.

[ZhihengNing]

just use the formula mentioned in the document can not work