unexpected “Double exponent: use braces to clarify”

The following throws a double exponent error in v3 but doesn't in v2 (or "real" LaTeX).

 \begin{align*} (E^{\sim })^{\bullet } = (R\pi _{*}f^{*}T_{\mathcal{U^{\sim }}^{\operatorname {etw}}/\mathcal{B^{\sim }}^{\operatorname {etw}}}^{\log })^{\vee } \rightarrow \mathcal{L}^{\log }_{M^{\sim }/\mathcal{MB^{\sim }}} \end{align*}

A more minimal example: \mathbf{x^x}^x