Error "underfull \hbox(\badness 10000)", using visual studio code with Latex extension

Question

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage[english]{babel}
\usepackage[]{amsthm} %lets us use \begin{proof}
\usepackage[]{amssymb} %gives us the character \varnothing
\usepackage[fleqn]{amsmath}
\usepackage{amsfonts}
\begin{document}
\maketitle
\subsection*{2. P18. Exercise 3:}
Assume we have a fair eight-sided die with the numbers 1, 2, 3, 3, 4, 5, 5, 5 on its sides.
What is the probability that each of the numbers 1 through 5 will be rolled? 
If we roll two of these dice, what is the range of possible totals of the values showing 
on the two dice? What is the chance that each of the numbers in this range will be rolled?\\

Answer 1

Please test this code:

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage[english]{babel}
\usepackage[]{amsthm} %lets us use \begin{proof}
\usepackage[]{amssymb} %gives us the character \varnothing
\usepackage[fleqn]{amsmath}
\usepackage{amsfonts}
\title{Test}
\author{None}
\begin{document}
\maketitle
\subsection*{2. P18. Exercise 3:}
Assume we have a fair eight-sided die with the numbers 1, 2, 3, 3, 4, 5, 5, 5 on its sides.
What is the probability that each of the numbers 1 through 5 will be rolled? 
If we roll two of these dice, what is the range of possible totals of the values showing 
on the two dice? What is the chance that each of the numbers in this range will be rolled?\par

\noindent Test
\end{document}

Then replace \par with \\ and compile again.

There is no warning in the first case in my version, but there is in second case.

\\ is something you have to avoid inside paragraphs of text. It is used inside tabulars or similar environments but not inside lines of text.

For more see here: https://tex.stackexchange.com/a/82666/120578