Mi bibliografía no se actualiza al cambiar de estilo

Question

Hay algún problema con mi bibliografía que no puedo resolver.

Cuando lo compilo, aparece este mensaje de error:

BibTeX: Ilegal, otro comando \bibstyle: \bibstyle: {plain}.

Además, no actualiza el estilo de la bibliografía cuando lo cambio.

Este es mi principal:

\documentclass{article}

% Importing settings from our file "setup.sty"
\usepackage{setup}
\usepackage{natbib}  

% Beginning of document
\begin{document}

% Inserting title page
\import{./}{title}

% Defining front matter settings 
\frontmatter

% Abstract 
\begin{abstract}
    \import{./Sections/}{0_abstract}
\end{abstract}
\clearpage


% Inserting table of contents
\tableofcontents

% Inserting list of figures & list of tables
\listoffigures
\listoftables

% Defining main matter settings 
\mainmatter


%Sections
\import{./Sections/}{1_introduction}
\import{./Sections/}{2_method}
\import{./Sections/}{3_results}
\import{./Sections/}{4_discussion}
\import{./Sections/}{5_conclusion}

% Inserting bibliography
\newpage
\bibliographystyle{plain}
\bibliography{references}

% Inserting appendix with separate settings
\addappendix

% End of document
\end{document}

Mi archivo de referencia está aquí:

@ONLINE {Supervised,
    author    = "Andrew Ng",
    title     = "CS229 Lecture notes",
    publisher = "Stanford",
    url       = "http://www.cs.bu.edu/~hwxi/GitHub/ATS-Postiats-contrib/projects/LARGE/ML/CS229/cs229.stanford.edu/notes/cs229-notes1.pdf",
    urldate   = "2020-09-07"
}

@article{ML_def,
    author =       "A.L. Samuel",
    title =        "{Some studies in machine learning using the game of checker}. ({English})",
    journal =      "IBM J. Res. Develop.",
    volume =       "3",
    number =       "3",
    pages =        "210--229",
    year =         "1959"
}
@book{Mitchell, 
    place={New York}, 
    title={Machine Learning}, 
    publisher={McGraw-Hill Education}, 
    author={Mitchell, Tom M.}, 
    year={1997}
}

@book{Definitions, 
    place={Amsterdam}, 
    title={Data Analyticsfor Intelligent Transportation Systems}, 
    publisher={Elsevier}, 
    author={Mashrur Chowdhury and Amy Apon and Kakan Dey}, 
    year={2017}
}

@book{SupMet, 
    place={Amsternam}, 
    title={Information Security Analytics}, 
    publisher={Elsevier}, 
    author={M.Talabis and R. McPherson and I. Miyamoto and J. Martin and D. Kaye}, 
    year={2014}
}

@book{Manufacturing, 
    place={Singapore}, 
    title={Groover's Principles of Modern Manufacturing}, 
    publisher={Wiley}, 
    author={Mikell P. Groover}, 
    year={2016}
}