3
\label{...} had to be after caption or referable counter in a table (which aren't present in your table).
Document class article doesn't define \chapter{...} . For it you neeed to use report or book document class (or other similar package, for example memoir)
\documentclass{article}
\usepackage{lmodern}
\usepackage[T1]{fontenc}
\usepackage{microtype}
\...
1
There are many issues with the code you've shown, especially your use of \multicolumn. The multicol package is not needed for this command which is a command for tabular material; the multicol package is for making multicolumn text outside of a table.
For this sort of table you don't want to use a table environment. The table environment turns its contents ...
1
You'll obtain what you want adding \leavevmode just after`\subsubsection' and removing the empty item:
\documentclass{article}
\usepackage{titlesec}
\usepackage{enumitem}
\usepackage{multicol}
\titleformat{\subsubsection}[runin]
{\bfseries}
{}
{0em}
{}
\begin{document}
\subsubsection{Subsubsection}\leavevmode
\begin{multicols}{2}
\begin{itemize}[...
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