[SVG][mathtools] multlined in aligned rendering poorly

Here's a rather involved real world use case:

\begin{equation}
 \begin{aligned}
[t] T_{{\mathbf{u}}, x} {\mathcal{V}}&= \begin{multlined}[t][.7\linewidth] \left\{ (\dot{{\mathbf{u}}}, \dot{x}) \in T_{\mathbf{u}}{\mathcal{U}}\times T_x {\mathbb{P}}^n\mathbin{|}\right. \\
 \left. \forall i, f_i \left( (\mathbf{1}_{\mathcal{U}}+ t \dot{u}_i + o(t))^{-1} (x+t \dot{x} + o(t)) \right) = o(t) \text{ as } t\to 0 \right\} \end{multlined}\\
 &= \left\{ (\dot{{\mathbf{u}}}, \dot{x}) \in T_{\mathbf{u}}{\mathcal{U}}\times T_x {\mathbb{P}}^n\mathbin{|}\forall i, f_i\left(x + t( \dot{x} - \dot{u}_i x) \right) = o(t) \text{  as } t\to 0 \right\}\\
 &= \left\{ (\dot{{\mathbf{u}}}, \dot{x}) \in T_{\mathbf{u}}{\mathcal{U}}\times T_x {\mathbb{P}}^n\mathbin{|}\forall i, \mathrm{d}_x f_i (\dot{x}) = \mathrm{d}_x f_i( \dot{u}_i x) \right\}. \end{aligned} \tag{17}\cssId{texmlid43}{}
\end{equation}

On https://www.mathjax.org/#demo, the SVG output renders poorly:

For comparison, the CSS output is: