`Incompatible glue units` error when modifying the `muskip` around an align environment

Question

I have a long equation which I am trying to fit into a single line:

\documentclass[a4paper,11pt,oneside]{article}
%%% DOCUMENT SETUP %%%
\PassOptionsToPackage{medium}{titlesec}
% packages and configurations come here (see list below).
\graphicspath{{images/}}
\title{My title}
\author{Myself}
\date{\today{}}
\begin{document}
\maketitle
\newcommand{\indicator}[1]{\mathbbm{1}_{{#1}}}
\newcommand{\sgn}{\mathrm{sgn}}
\begin{align}
    \Lambda=
    \frac{1}{x}\left(
        \indicator{z\geq0}
        -e^{-xt}\Phi\left(\beta_0\right)
        +\frac{e^{-zy}}{2}\left(
            e^{-zp}\left(\frac{y}{p}-1\right)\Phi\left(\sgn(z)\beta_1\right)
            -e^{zp}\left(\frac{y}{p}+1\right)\Phi\left(-\sgn(z)\beta_2\right)
        \right)
    \right)
\end{align}
\end{document}

Based on this answer, I have tried to compact the equation by modifying the values of \thinmuskip and \medmuskip:

\begingroup
\setlength{\thinmuskip}{0mu}
\setlength{\medmuskip}{0mu}
\begin{align}
    \Lambda=
    \frac{1}{x}\left(
        \indicator{z\geq0}
        -e^{-xt}\Phi\left(\beta_0\right)
        +\frac{e^{-zy}}{2}\left(
            e^{-zp}\left(\frac{y}{p}-1\right)\Phi\left(\sgn(z)\beta_1\right)
            -e^{zp}\left(\frac{y}{p}+1\right)\Phi\left(-\sgn(z)\beta_2\right)
        \right)
    \right)
\end{align}
\endgroup

However I am getting the following errors:

! Incompatible glue units.               \setlength{\thinmuskip}{0mu}
! Illegal unit of measure (pt inserted). \setlength{\medmuskip}{0mu}

Moreover, the string u! appears in my output at the place where the group begins.

There are other questions on this site about this sort of error, such as this, but it seems unrelated to the problem at hand.

What is causing my code to fail here?

Edit: packages/settings for my document

\usepackage{lmodern}
\usepackage[T1]{fontenc}
\usepackage{bbm}
\usepackage{bm}
\usepackage[top=1in, bottom=1in, left=1in, right=1in]{geometry}
\usepackage{graphicx}
\usepackage[colorlinks=true,allcolors=blue]{hyperref}
\usepackage[authoryear]{natbib}
\usepackage{titlesec}
\usepackage[dvipsnames]{xcolor}
\usepackage[normalem]{ulem}
\usepackage{soul}
\usepackage{color}
\usepackage{booktabs}
\usepackage[textsize=footnotesize,tickmarkheight=3pt]{todonotes}
\usepackage{setspace}
% MATHS %
\usepackage{amsmath}
\usepackage{amsthm}
\usepackage{amssymb}
\usepackage{bigints}
\usepackage{mathrsfs}
\usepackage{xfrac}
\usepackage{yfonts}
\usepackage{mathtools}
\usepackage{upgreek}
\usepackage{nccmath}
\usepackage{scalerel}
\usepackage{accents}
\usepackage{nicefrac}
\usepackage{mathtools}
\usepackage{subcaption}
\usepackage[labelfont=bf]{caption}
\usepackage{changepage}
\usepackage{enumitem}
\usepackage{eurosym}
\usepackage{indentfirst}
\usepackage{bibentry}
\usepackage{pifont}
\setlength\parindent{0pt}
\bibliographystyle{myauthordate3}
\setcitestyle{authoryear,round,semicolon,}
\titleformat{\paragraph}[hang]
{\normalfont\normalsize\bfseries}{}{1em}{}
\titlespacing{\paragraph}{0pt}{3.25ex plus 1ex minus .2ex}{1.5ex plus .2ex}
\titleformat{\subparagraph}
{\normalfont\normalsize\bfseries}{\thesubparagraph}{1em}{}
\titlespacing{\subparagraph}{\parindent}{3.25ex plus 1ex minus .2ex}{.75ex plus .1ex}
\makeatletter
\def\today{%
    \two@digits{\the\day}-%
    \ifcase\month\or%
    Jan\or Feb\or Mar\or Apr\or May\or Jun\or%
    Jul\or Aug\or Sep\or Oct\or Nov\or Dec\fi-%
    \number\year%
}
\makeatother
\newcommand{\indicator}[1]{\mathbbm{1}_{{#1}}}
\newcommand{\sgn}{\mathrm{sgn}}
\makeatletter
\newcommand{\vast}{\bBigg@{4}}
\newcommand{\Vast}{\bBigg@{5}}
\makeatother

Answer 1

The scalerel package loads calc. Once the latter package is called, it's not possible to set muskips with \setlength.

Just do

\thinmuskip=0mu
\medmuskip=0mu

instead of \setlength.

Answer 2

There's been a lot of thought put into the default spacing. Instead of changing that, I would split the equation into two:

\documentclass[a4paper,11pt]{article}
\usepackage[margin=1in]{geometry}
\usepackage{amsmath}
\usepackage{bbm}
\newcommand{\indicator}[1]{\mathbbm{1}_{\{#1\}}}
\DeclareMathOperator{\sgn}{sgn}
\begin{document}
\begin{multline}
    \Lambda=
    \frac{1}{x}\biggl(
        \indicator{z\geq0}
        -e^{-xt}\Phi(\beta_0)\\
        +\frac{e^{-zy}}{2}\Bigl(
            e^{-zp}\Bigl(\frac{y}{p}-1\Bigr)\Phi(\sgn(z)\beta_1)
            -e^{zp}\Bigl(\frac{y}{p}+1\Bigr)\Phi(-\sgn(z)\beta_2)
        \Bigr)
    \biggr)
\end{multline}
\end{document}

This renders as:

I've also changed out the \left and \right, since they aren't quite optimal in this case (I can't find the appropriate Q&A at the moment).

A postscript on minimal examples: we only need amsmath and bbm in order to compile the example. We only need the document class options and geometry to determine the size of the avaiable text area. Everything else makes your example (1) more difficult to follow and (2) not compilable as a single block of code.