Update of TikZ/pgf has broken user-defined command

Question

A recent update of TikZ/pgf seems to have broken a newly defined command that came out of an earlier question of mine about crossing out terms in an equation.

Here's an MWE that illustrates the problem:

\documentclass{article}

\usepackage{amsmath}
\usepackage{tikz}
\usetikzlibrary{calc,positioning,tikzmark}

\newif\ifCancelToOverlay
\tikzset{CancelTo/.is family,
 CancelTo,
 angle/.initial=60,
 name/.initial=tmp,
 node/.style={},
 arrow/.style={->},
 topoffs/.initial=2pt, 
 nodeaboveoffs/.initial=1pt,
 nodeleftoffs/.initial=0pt,
 overlay/.is if=CancelToOverlay,
 overlay=true  
}

\newcommand{\CancelTo}[3][]{\bgroup\tikzset{CancelTo/.cd,#1}
\tikzmarknode{\pgfkeysvalueof{/tikz/CancelTo/name}}{#3}
\begin{tikzpicture}[overlay,remember picture]
 \draw[/tikz/CancelTo/arrow] let \p1=($(\pgfkeysvalueof{/tikz/CancelTo/name}.north)-(\pgfkeysvalueof{/tikz/CancelTo/name}.south)$),\n1={0.5*\y1*cot(\pgfkeysvalueof{/tikz/CancelTo/angle})},\n2={\y1/sin(\pgfkeysvalueof{/tikz/CancelTo/angle})} 
 in ([xshift=-\n1]\pgfkeysvalueof{/tikz/CancelTo/name}.south) -- ++ (\pgfkeysvalueof{/tikz/CancelTo/angle}:\n2+\pgfkeysvalueof{/tikz/CancelTo/topoffs}) 
 node[above left=\pgfkeysvalueof{/tikz/CancelTo/nodeaboveoffs} and \pgfkeysvalueof{/tikz/CancelTo/nodeleftoffs},inner sep=0pt,font=\scriptsize,/tikz/CancelTo/node] (tmplabel) {#2};
 \path let \p1=($(tmplabel.north east)-(\pgfkeysvalueof{/tikz/CancelTo/name}.east)$) in
 \pgfextra{\ifCancelToOverlay
 \xdef\mydist{0pt}
 \else 
 \xdef\mydist{\x1}
 \fi};
\end{tikzpicture}\egroup\vphantom{\cancelto{#2}{#3}}\hspace{\mydist}}

\input{math-defs}

\begin{document}
  \begin{equation*}
     \CancelTo[nodeleftoffs=-11pt]{ignore}{\frac{x^2}{4}}
  \end{equation*}
\end{document}

This code used to work, but now produces

! Package pgf Error: No shape named tmp is known.

See the pgf package documentation for explanation.
Type  H <return>  for immediate help.
 ...                                              

l.39 ...nodeleftoffs=-11pt]{ignore}{\frac{x^2}{4}}

I'm running:

• pdfTeX, Version 3.14159265-2.6-1.40.20 (TeX Live 2019)
• pgf 2019/08/03 v3.1.4b (3.1.4b)
• tikz 2019/08/03 v3.1.4b (3.1.4b)