How do I debug what is causing tagging related warnings and how do I fix them?

I have a sty file which defines my institution's dissertation format. I have for the most part been able to get it to work with tagging (via TexLive 2025, LuaLaTeX and tweaking code) for accessibility. Likewise, I have gone from TaggedPDF reporting errors, to the document compiling with just some warnings. Accessibility checking (via Foxit) gives "Lbl and LBody - Failed" which I narrowed down to \chapter and \section macros.

For posterity, I had to tweak the \tableofcontents macro from:

\newlength\singlespacelength
\newlength\doublespacelength
\newlength\triplespacelength

\setlength\singlespacelength{15\p@}
\setlength\doublespacelength{26\p@}
\setlength\triplespacelength{40\p@}

\newcommand\startsinglespace{\setlength\baselineskip{\singlespacelength}}
\newcommand\startdoublespace{\setlength\baselineskip{\doublespacelength}}

\def\typesetHeading#1{{\normalfont\large{#1}}}
\def\intro{\clearpage \thispagestyle{intropage}
  \global\@topnum\z@ \@afterindenttrue \secdef\@chapter\@schapter }
\renewcommand\contentsname{TABLE OF CONTENTS}
\newcommand\contentsnameLC{Table of Contents}

\renewcommand\tableofcontents{%
   \intro*{\typesetHeading\bf\contentsnameLC
   \@mkboth{{\contentsnameLC}}{{\contentsnameLC}}}%
     \startsinglespace
     \@starttoc{toc}
     \startdoublespace
}

to

% ... other definitions left alone

\renewcommand\tableofcontents{%
    \if@openright\cleardoublepage\else\clearpage\fi
    \begingroup
    \startsinglespace
    \centering
    {\normalfont\large\bfseries \contentsnameLC}%
    \@mkboth{{\contentsnameLC}}{{\contentsnameLC}}%
    \par\vskip\medskipamount
    \@starttoc{toc}%
    \endgroup
}

Which fixed the errors. Now I am facing a tougher problem, the chapter macros. Unlike the other commands which I was able to get working, the chapter macros are a lot more coupled/complex, and I cannot tell where exactly are things breaking. I would appreciate instruction on how to begin to debug this, or working chapter macros that achieve the same thing (visually).

\def\chapter{\clearpage  \thispagestyle{chappage}
  \global\@topnum\z@ \@afterindenttrue \secdef\@chapter\@schapter }%\pagestyle{plain}

\def\@chapter[#1]#2{
%% Chapters are necessary, so checking secnumdepth is immaterial.
  \refstepcounter{chapter}%
  \ifapp
    \ifnum\value{chapter}=1
      \addtocontents{toc}{\vskip 1.0em %plus 1pt
         \hskip -\parindent \appendicesname\hfill%
      \vskip 0.25em
     \rm}
    \else
      {}
    \fi
  \else
    \ifnum\value{chapter}=1
    % Moving away from roman numerals
%     \pagenumbering{arabic}
      \pagestyle{plain}
            \addtocontents{toc}{\vskip 0.25em
        \rm}
    \fi
  \fi

  \ifnum \c@secnumdepth >\m@ne
    \typeout{\@chapapp\space\thechapter.}
    \addcontentsline{toc}{chapter}{\protect\numberline{\thechapter.}#1}%
  \else
    \addcontentsline{toc}{chapter}{#1}
  \fi
  \chaptermark{#1}%
  \@makechapterhead{#2}%
%  \pagestyle{reset}
}

% Chapter # is 2in from top, followed by 2 lines, followed by
% the title, 4 lines, and then the text.
\def\@makechapterhead#1{
    {

        % Change Chapter headings from 2in. to 1in.
        %\vspace*{0.25in}
        \vspace*{-0.75in}
        \parindent \z@ \raggedright \reset@font
        \ifnum \c@secnumdepth >\m@ne%
            \center\typesetHeading{\bf\@chapapp{} \bf\thechapter}%
            %\par
            %\vskip 30pt
        \fi
        \begin{center}
            % Remove Bold from Chapter Headings
            %\large\boldcmd\typesetChapterTitle{#1}
            \vskip -20pt
            \typesetChapterTitle{#1}
            %\par
        \end{center}
    \nobreak
    %\vskip 15\p@ % Too much space between chapter title and body
    }
}

\def\@schapter#1{%
     \@makeschapterhead{#1}%
}
% Placement of the Chapter headings
\def\@makeschapterhead#1{
    % Change heading in TOC, LOF, LOT, and Aknowledgements from 2in. to 1in.
    \vspace*{-0.5in}
    {
        \parindent \z@ \raggedright
        \reset@font
        \begin{center}
            \large\boldcmd\typesetChapterTitle{#1}
            \par
        \end{center}
        \nobreak
        % Reduce the spacing between the chapter heading and title
        \vskip 15\p@
    }
}