Lambda not rendering in MDPI Journal

Question

Why the lambda is not rendering in equation (2) below? What was my mistake there? You will need the Definitions folder from the MDPI journal template to run this.

\documentclass[energies,article,submit,pdftex,moreauthors]{Definitions/mdpi} 
\usepackage[utf8]{inputenc}
\title{test_lambda}
\begin{document}
\maketitle
\section{Introduction}
Like this, it works:
\begin{equation}
    \lambda
\end{equation}
But here, it does not work:
\begin{equation}
        \mathbf{w_{out} = r^{\mathit{T}}M(M^{\mathit{T}}M + \mathit{\lambda}^{\mathrm{2}}I)^{-1}},
\end{equation}
And like this $\lambda$, it also works.
\end{document}

Output:

EDIT: Link to get the MDPI template:

Template

Answer 1

The font does not include a bold math version of lambda. If you can live with a normal math lambda, you could use \mathnormal to switch back to the normal weight:

\documentclass[energies,article,submit,pdftex,moreauthors]{Definitions/mdpi} 
\usepackage[utf8]{inputenc}
\firstpage{1} 
\makeatletter 
\setcounter{page}{\@firstpage} 
\makeatother
\pubvolume{1}
\issuenum{1}
\articlenumber{0}
\pubyear{2023}
\copyrightyear{2023}
%\externaleditor{Academic Editor: Firstname Lastname}
\datereceived{ } 
\daterevised{ } % Comment out if no revised date
\dateaccepted{ } 
\datepublished{ } 
%\datecorrected{} % For corrected papers: "Corrected: XXX" date in the original paper.
%\dateretracted{} % For corrected papers: "Retracted: XXX" date in the original paper.
\hreflink{https://doi.org/} % If needed use \linebreak
\Title{Title}
% MDPI internal command: Title for citation in the left column
\TitleCitation{Title}
% Author Orchid ID: enter ID or remove command
\newcommand{\orcidauthorA}{0000-0000-0000-000X} % Add \orcidA{} behind the author's name
%\newcommand{\orcidauthorB}{0000-0000-0000-000X} % Add \orcidB{} behind the author's name
% Authors, for the paper (add full first names)
\Author{Firstname Lastname $^{1,\dagger,\ddagger}$\orcidA{}, Firstname Lastname $^{2,\ddagger}$ and Firstname Lastname $^{2,}$*}
%\longauthorlist{yes}
% MDPI internal command: Authors, for metadata in PDF
\AuthorNames{Firstname Lastname, Firstname Lastname and Firstname Lastname}
% MDPI internal command: Authors, for citation in the left column
\AuthorCitation{Lastname, F.; Lastname, F.; Lastname, F.}
% If this is a Chicago style journal: Lastname, Firstname, Firstname Lastname, and Firstname Lastname.
% Affiliations / Addresses (Add [1] after \address if there is only one affiliation.)
\address{%
$^{1}$ \quad Affiliation 1; e-mail@e-mail.com\
$^{2}$ \quad Affiliation 2; e-mail@e-mail.com}
% Contact information of the corresponding author
\corres{Correspondence: e-mail@e-mail.com; Tel.: (optional; include country code; if there are multiple corresponding authors, add author initials) +xx-xxxx-xxx-xxxx (F.L.)}
% Current address and/or shared authorship
\firstnote{Current address: Affiliation 3.} 
\secondnote{These authors contributed equally to this work.}
\begin{document}
\maketitle
\section{Introduction}
Like this, it works:
\begin{equation}
    \lambda
\end{equation}
But here, it does not work:
\begin{equation}
        \mathbf{w_{out} = r^{\mathit{T}}M(M^{\mathit{T}}M + \mathnormal{\lambda}^{\mathrm{2}}I)^{-1}},
\end{equation}
And like this $\lambda$, it also works.
\end{document}