how generation of .bbl files happen when working with templates downloaded from internet

Question

I use a template available https://www.overleaf.com/latex/templates/eusflat-2019-template/jmqvcrhkqhgx . The code which I am editing is

\documentclass{eusflat2019}
\title{\bf Paper Title}
\author{{\bf Author1$^1$} , {\bf Author2 $^2$} , {\bf Author3 $^3$}\\
$^1$CSE Department,University, email \\ $^2$CSE Department,Faculty, university, email \\
$^3$CSE Department,Faculty,University  G, email }
\usepackage{parskip}
\usepackage{graphicx}
\usepackage{url}
\usepackage{breakurl}
\usepackage{hyperref}
\setlength{\parskip}{0pt}
\setlength{\parindent}{1mm}
\begin{document}
\maketitle
\begin{abstract}
\end{abstract}

\section{Title}
some randomg paragraph \cite{resource1} some random text.
some thing random some thing random.something random.
 \bibliographystyle{unsrt} 
\bibliographystyle{eusflat2019} 
\bibliography{BIBeusflat2019}
\end{document}

now I go and add another item manually in the BIBeusflat2019.bib file and I use a doi to bib converter online https://www.doi2bib.org/bib/http://dx.doi.org/10.4236/jis.2015.62015 and add the entry in my .bib file.

@article{Sari2015,
  doi = {10.4236/jis.2015.62015},
  url = {https://doi.org/10.4236/jis.2015.62015},
  year = {2015},
  publisher = {Scientific Research Publishing,  Inc, },
  volume = {06},
  number = {02},
  pages = {142--154},
  author = {Arif Sari},
  title = {A Review of Anomaly Detection Systems in Cloud Networks and Survey of Cloud Security Measures in Cloud Storage Applications},
  journal = {Journal of Information Security}
}

now I cite the article and my new .tex file looks as following

\documentclass{eusflat2019}
\title{\bf Paper Title}
\author{{\bf Author1$^1$} , {\bf Author2 $^2$} , {\bf Author3 $^3$}\\
$^1$CSE Department,University, email \\ $^2$CSE Department,Faculty, university, email \\
$^3$CSE Department,Faculty,Uniersity G, email }
\usepackage{parskip}
\usepackage{graphicx}
\usepackage{url}
\usepackage{breakurl}
\usepackage{hyperref}
\setlength{\parskip}{0pt}
\setlength{\parindent}{1mm}
\begin{document}
\maketitle
\begin{abstract}
\end{abstract}

\section{Title}
some randomg paragraph \cite{resource1} some random text.
some thing random some thing random.something\cite{Sari2015} random.
 \bibliographystyle{unsrt} 
\bibliographystyle{eusflat2019} 
\bibliography{BIBeusflat2019}

\end{document}

Now when I try to compile the pdf for the preview then in Tex Studio I see an error

Misplaced alignment tab character &. \newblock {\em Computers &

so what I see in one of the references which previously had & in the bibliography entry is generated as & and this gives me an error. The entry in which it gave me this problem is following

\bibitem{CHEN20052617}
Wun-Hwa Chen, Sheng-Hsun Hsu, and Hwang-Pin Shen.
\newblock Application of svm and ann for intrusion detection.
\newblock {\em Computers & Operations Research}, 32(10):2617 -- 2634, 2005.
\newblock Applications of Neural Networks.

in file EUSFLAT2019_template.bbl (this file is automatically generated I did not do anything to generate it).The above entry was generated in EUSFLAT2019_template.bbl automatically. I manually go and edit the error location from & to \& and the error is gone.So new entry now looks like

\bibitem{CHEN20052617}
Wun-Hwa Chen, Sheng-Hsun Hsu, and Hwang-Pin Shen.
\newblock Application of svm and ann for intrusion detection.
\newblock {\em Computers \& Operations Research}, 32(10):2617 -- 2634, 2005.
\newblock Applications of Neural Networks.

Now I keep working and later on I add some more citations or do some other editing then this happens The entry in which this happened was following in BIBeusflat2019.bib file

@article{CHEN20052617,
    title = "Application of SVM and ANN for intrusion detection",
    journal = "Computers & Operations Research",
    volume = "32",
    number = "10",
    pages = "2617 - 2634",
    year = "2005",
    note = "Applications of Neural Networks",
    issn = "0305-0548",
    doi = "https://doi.org/10.1016/j.cor.2004.03.019",
    url = "http://www.sciencedirect.com/science/article/pii/S0305054804000711",
    author = "Wun-Hwa Chen and Sheng-Hsun Hsu and Hwang-Pin Shen",
    keywords = "Intrusion detection, Artificial neural networks, Support vector machine",
    abstract = "The popularization of shared networks and Internet usage demands increases attention on information system security, particularly on intrusion detection. Two data mining methodologies—Artificial Neural Networks (ANNs) and Support Vector Machine (SVM) and two encoding methods—simple frequency-based scheme and tf×idf scheme are used to detect potential system intrusions in this study. Our results show that SVM with tf×idf scheme achieved the best performance, while ANN with simple frequency-based scheme achieved the worst. The data used in experiments are BSM audit data from the DARPA 1998 Intrusion Detection Evaluation Program at MIT's Lincoln Labs."
}

so now I manually go and change & here to \&

and I compile the the program again to generate pdf. Now I still get the same error in file EUSFLAT2019_template.bbl \newblock {\em Computers & Operations Research}, 32(10):2617 -- 2634, 2005.

Misplaced alignment tab character &. \newblock {\em Computers &

I will go and do change & to \&. What I want to know is this kind of behavior with editing a usual thing or I need to check some thing else.Because adding citation entries or editing the text some times generates this situation. I previously have done manual sorting of citations to use in this template which I answered here sequence number in bibliographic text how is serial number decided could this problem be related to this? I basically want to know when using templates then the generation of .bbl files if it is automatic, then how does it happen. I want to read more about it.