Tikz arrows/node not displaying properly with Beamer

Question

Working on a presentation where I need to have explanations pointing to parts of an equation with an arrow.
Tried copy-pasting the following 2 examples:
https://texample.net/tikz/examples/beamer-arrows/
How to draw good arrows explaining parts of equation? (the solution provided by jonalv to his own question).

Here is how they are displaying in my slides individually:

It seems all the arrows are pointing/coming out of a single node instead of several. Can someone explain why that is?

Here is my settings file:

\documentclass[hyperref={unicode=true}]{beamer}

\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage[russian]{babel}

\usepackage{lmodern}
\usepackage{tempora} % this supports Cyrillic
\usepackage{newtxmath}
\usepackage{bm}
\usepackage{comment}

\usefonttheme{serif}
\usecolortheme{default}
\usefonttheme{professionalfonts}
\setbeamertemplate{navigation symbols}{}
\setbeamertemplate{caption}[numbered]
\usepackage{appendixnumberbeamer}

\usepackage [section]{placeins}
\usepackage{graphicx} % for pdf, bitmapped graphics files
\usepackage{epsfig} % for postscript graphics files
\usepackage{epstopdf}
\usepackage[caption=false]{subfig}
\usepackage{xcolor}
\usepackage{array}
\usepackage{amsmath}
\usepackage{amssymb}  % assumes amsmath package installed
\usepackage{amsfonts}  % assumes amsmath package installed
\usepackage{bm} % for bold math, improved
\usepackage{cancel}
\usepackage{mathrsfs}  % adds \mathscr for nice capital letters

\usepackage{tikz}
\usetikzlibrary{calc}

\newcommand{\tikzmark}[1]{\tikz[baseline,remember picture] \coordinate (#1) {};}

\usepackage{tabularx}

\everymath{\displaystyle}

\usepackage{subfig}
\usepackage{cancel}
\usepackage{mathtools}
\newcommand{\sign}{\operatorname{sgn}}
\DeclarePairedDelimiter{\homd}{\lceil}{\rfloor}
\newcommand{\R}{\ensuremath{\mathbb{R}}}
\newcommand\Ccancel[2][black]{\renewcommand\CancelColor{\color{#1}}\cancel{#2}}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\graphicspath{{Figs/}}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\beamertemplatenavigationsymbolsempty
\usetheme{Boadilla}

\makeatletter
\defbeamertemplate*{footline}{my theme}{
    \leavevmode%
    \hbox{%
    \begin{beamercolorbox}[wd=.9\paperwidth,ht=2.25ex,dp=1ex,center]{title in head/foot}%
        \usebeamerfont{title in head/foot}Управление по выходу параметрическим неопределенным нелинейным объектом с нарушением условий согласования
    \end{beamercolorbox}%
    \begin{beamercolorbox}[wd=.1\paperwidth,ht=2.25ex,dp=1ex,right]{date in head/foot}%
        \usebeamerfont{date in head/foot}{}\hspace*{2em}
        \insertframenumber{} / \inserttotalframenumber\hspace*{2ex}
    \end{beamercolorbox}}%
}
\makeatother

\setbeamertemplate{bibliography entry title}{}
\setbeamertemplate{bibliography entry location}{}
\setbeamertemplate{bibliography entry note}{}

\graphicspath{{Figs/}{../Figs/}}
\usepackage{subfiles}

% ------------------- PRESENTATION INFO ---------------------------
\title{ИТЕРАТИВНАЯ ПРОЦЕДУРА СИНТЕЗА АДАПТИВНОГО УПРАВЛЕНИЯ НА БАЗЕ ИНТЕГРАЛЬНОГО АЛГОРИТМА АДАПТАЦИИ}

\date{}
\author[Олег Суздалев, R3435]{\large{\textbf{Докладчик: Суздалев Олег Димитрий}\\
Научный руководитель: Герасимов Д.Н., к.т.н.\\}}

\institute{\large{\centering\\ Университет ИТМО \\ Факультет СУиР \vspace{1em} }}

Thank you in advance!

Answer 1

I use only the second example you were talking about. I modified the command \tikzmark (mainly replacing \coordinate with \node which is more natural in the context) and cleaned the code slightly.

The whole code is pasted below. The first part is your preamble that I didn't touch. My modifications start after the line of percentages.

\documentclass[hyperref={unicode=true}]{beamer}

\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage[russian]{babel}

\usepackage{lmodern}
\usepackage{tempora} % this supports Cyrillic
\usepackage{newtxmath}
\usepackage{bm}
\usepackage{comment}

\usefonttheme{serif}
\usecolortheme{default}
\usefonttheme{professionalfonts}
\setbeamertemplate{navigation symbols}{}
\setbeamertemplate{caption}[numbered]
\usepackage{appendixnumberbeamer}

\usepackage [section]{placeins}
\usepackage{graphicx} % for pdf, bitmapped graphics files
\usepackage{epsfig} % for postscript graphics files
\usepackage{epstopdf}
\usepackage[caption=false]{subfig}
\usepackage{xcolor}
\usepackage{array}
\usepackage{amsmath}
\usepackage{amssymb}  % assumes amsmath package installed
\usepackage{amsfonts}  % assumes amsmath package installed
\usepackage{bm} % for bold math, improved
\usepackage{cancel}
\usepackage{mathrsfs}  % adds \mathscr for nice capital letters


\usepackage{tabularx}

\everymath{\displaystyle}

\usepackage{subfig}
\usepackage{cancel}
\usepackage{mathtools}
\newcommand{\sign}{\operatorname{sgn}}
\DeclarePairedDelimiter{\homd}{\lceil}{\rfloor}
\newcommand{\R}{\ensuremath{\mathbb{R}}}
\newcommand\Ccancel[2][black]{\renewcommand\CancelColor{\color{#1}}\cancel{#2}}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\graphicspath{{Figs/}}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\beamertemplatenavigationsymbolsempty
\usetheme{Boadilla}

\makeatletter
\defbeamertemplate*{footline}{my theme}{
    \leavevmode%
    \hbox{%
    \begin{beamercolorbox}[wd=.9\paperwidth,ht=2.25ex,dp=1ex,center]{title in head/foot}%
        \usebeamerfont{title in head/foot}Управление по выходу параметрическим неопределенным нелинейным объектом с нарушением условий согласования
    \end{beamercolorbox}%
    \begin{beamercolorbox}[wd=.1\paperwidth,ht=2.25ex,dp=1ex,right]{date in head/foot}%
        \usebeamerfont{date in head/foot}{}\hspace*{2em}
        \insertframenumber{} / \inserttotalframenumber\hspace*{2ex}
    \end{beamercolorbox}}%
}
\makeatother


\setbeamertemplate{bibliography entry title}{}
\setbeamertemplate{bibliography entry location}{}
\setbeamertemplate{bibliography entry note}{}

\graphicspath{{Figs/}{../Figs/}}
\usepackage{subfiles}


% ------------------- PRESENTATION INFO ---------------------------
\title{ИТЕРАТИВНАЯ ПРОЦЕДУРА СИНТЕЗА АДАПТИВНОГО УПРАВЛЕНИЯ НА БАЗЕ ИНТЕГРАЛЬНОГО АЛГОРИТМА АДАПТАЦИИ}

\date{}
\author[Олег Суздалев, R3435]{\large{\textbf{Докладчик: Суздалев Олег Димитрий}\\
Научный руководитель: Герасимов Д.Н., к.т.н.\\}}

\institute{\large{\centering\\ Университет ИТМО \\ Факультет СУиР \vspace{1em} }}


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\usepackage{tikz}
\usetikzlibrary{calc}

\newcommand{\tikzmark}[1]{%
  \begin{tikzpicture}[baseline, remember picture]
    \node[inner sep=0pt, outer sep=.5ex] (#1) {};
  \end{tikzpicture}
}

\begin{document}


\begin{frame}{Tests}

  This is the example ``How to draw good arrows explaining parts of
  equation?'' you were pointing to in the question.

  \vfill
  
  \hspace{4em}
  $\tikzmark{V}V
  = \tikzmark{Vp}V_p
  + \tikzmark{Vt}V_t\,\frac{fu\tikzmark{fu}}{fu_t\tikzmark{fut}}$

  \begin{tikzpicture}[overlay, remember picture,
    every node/.style={scale=.7, inner sep=3pt},
    spear/.style={->, blue, shorten <=3pt, shorten >=3pt}]
      
    \node
    (Ve) [below of=V, node distance=10em, anchor=west]
    {\textsf{distribution volume}};
    \node (Vpe) [below of=Vp, node distance=7em, anchor=west]
    {\textsf{volume water in plasma}};
    \node (Vte) [below of=Vt, node distance=4em, anchor=west]
    {\textsf{volume water in tissue}};
    \node (fue) [above right of=fu, node distance=4em, anchor=west]
    {\textsf{fraction unbound drug in plasma}};
    \node (fute) [right of=fut, node distance=4em, anchor=west]
    {\textsf{Fraction unbound drug in tissue}};
    
    \draw
    (Ve) edge[spear, out=175, in=-115] (V)
    (Vpe) edge[spear, out=180, in=-110] (Vp)
    (Vte) edge[spear, out=180, in=-105] (Vt)
    (fue) edge[spear, out=182, in=40] (fu)
    (fute) edge[spear, out=180, in=-20] (fut);
  \end{tikzpicture}
\end{frame}

\end{document}