istgame error on correct code

Code:

documentclass[12pt]{article}
usepackage{istgame}
usepackage{tikz}
usetikzlibrary{shapes,arrows.meta, positioning}
usepackage{enumitem}
usepackage{float}
usepackage[margin=1in]{geometry} 
usepackage{amsmath}
begin{document}
    begin{figure}[H]
        centering
        begin{istgame}[scale = 0.85, transform shape] %Cause of error
            setistNewNodeStyle{max}
            [regular polygon, regular polygon sides = 3]{1.75cm}
            setistNewNodeStyle{maxTerm}
            [regular polygon, regular polygon sides = 3, dashed]{1.75cm}
            setistNewNodeStyle{min}
            [regular polygon, regular polygon sides = 3, shape border rotate = 180]{1.75cm}
            defdistFactor{25};
            xtdistance{distFactor mm}{4*distFactor mm}
            istroot(bd)[max]<center>{$bd$}
            istb istb endist
            xtdistance{distFactor mm}{2*distFactor mm}
            istroot(cd)(bd-1)[min]<center>{$cd$}
            istb istb istb endist
            xtdistance{distFactor mm}{distFactor mm}
            istroot(ce)(cd-1)[max]<center>{$ce$}
            istb istb endist
            istroot(de)(ce-1)[min]<center>{$de$}
            istb endist
            istroot(dd)(de-1)[maxTerm]<center>{$dd$} endist
            istroot(be)(ce-2)[min]<center>{$be$} 
            istb endist
            istroot(bdRepeat)(be-1)[max]<center>{$bd$} 
            istbt{}{-1} istbt{}{0} endist %Error
        end{istgame}
    end{figure}
    begin{figure}[H]
        centering
        begin{istgame}
            setistNewNodeStyle{max}
            [regular polygon, regular polygon sides = 3]{1.75cm}
            setistNewNodeStyle{min}
            [regular polygon, regular polygon sides = 3, shape border rotate = 180]{1.75cm}
            setistNewNodeStyle{chance}
            [circle]{1.2cm}
            %xtShowTerminalNodes[box node, minimum size = 1cm]
            defdistFactor{20};
            xtdistance{distFactor mm}{4*distFactor mm}
            setxtarrowtips[blue, thick]
            istroot(0)[max]<center, blue>{1.5}
            istb[blue, ->-] istb endist
            xtdistance{distFactor mm}{2*distFactor mm}
            istroot(1)(0-1)[chance]<center, purple>{1.5}
            istb{0.5}[al] istb{0.5}[ar] endist
            istroot(2)(0-2)[chance]<center, purple>{$-0.5$}
            istb{0.5}[al] istb{0.5}[ar] endist
            xtdistance{distFactor mm}{distFactor mm}
            istroot(3)(1-1)[min]<center, red>{2}
            istbt{}{2} istbt{}{2} endist
            istroot(4)(1-2)[min]<center, red>{1}
            istbt{}{1} istbt{}{2} endist
            istroot(5)(2-1)[min]<center, red>{0}
            istbt{}{0} istbt{}{2} endist
            istroot(6)(2-2)[min]<center, red>{$-1$}
            istbt{}{-1} istbt{}{0} endist
        end{istgame}
    end{figure}
end{document}

Error message:

Package PGF Math Error: Unknown function `south' (in 'south'). istbt{}{-1} istbt{}{0} endist

Output:

The syntax is correct, yet I am getting an error for the line with the %Error comment. What is going on?

Edit: If I comment out the [scale = 0.85, transform shape] part, the error doesn’t appear. Why would an error be thrown then?

begin{istgame}[scale = 0.85] %%, transform shape] %Cause of error
    setistNewNodeStyle{max}
    [regular polygon, regular polygon sides = 3, 
    transform shape]{1.75cm}
    setistNewNodeStyle{maxTerm}
    [regular polygon, regular polygon sides = 3, dashed, 
    transform shape]{1.75cm}
    setistNewNodeStyle{min}
    [regular polygon, regular polygon sides = 3, shape border rotate = 180, 
    transform shape]{1.75cm}
    ...