Inconsistent latex bibliographic references

Question

I am having references appearing in different format each time. Sometimes it appear in the correct format (FirstnameFirstAuthor et al Year), and in other times it appear in different format (Firstauthor name second author name and thirdauthor name and year). You can see for the example below I am doing

\documentclass[a4paper,fleqn]{cas-sc}
\usepackage[authoryear,longnamesfirst]{natbib} 

\begin{document}

First citation is appearing correctly \cite{chen2018effective}, Second is correct also 
     \cite{deng2019user}, while last one is appearing in incorrect format \cite{liang2021unsupervised}

\bibliographystyle{cas-model2-names}
\bibliography{bmc_article}

\end{document}

Here are the three bibs entries in the bmc_article.bib file :

@article{chen2018effective,
  title={Effective and efficient user account linkage across location based social networks},
  author={Chen, Wei and Yin, Hongzhi and Wang, Weiqing and Zhao, Lei and Zhou, Xiaofang},
  booktitle={2018 IEEE 34th International Conference on Data Engineering (ICDE)},
  pages={1085--1096},
  year={2018},
  organization={IEEE}
}

@article{deng2019user,
  title={A user identification algorithm based on user behavior analysis in social networks},
  author={Deng, Kaikai and Xing, Ling and Zheng, Longshui and Wu, Honghai and Xie, Ping and Gao, Feifei},
  journal={IEEE Access},
  volume={7},
  pages={47114--47123},
  year={2019},
  publisher={IEEE}
}
@article{liang2021unsupervised,
  title={Unsupervised Large-Scale Social Network Alignment via Cross Network Embedding},
  author={Liang, Zhehan and Rong, Yu and Li, Chenxin and Zhang, Yunlong and Huang, Yue and Xu, Tingyang and Ding, Xinghao and Huang, Junzhou},
  booktitle={Proceedings of the 30th ACM International Conference on Information \& Knowledge Management},
  pages={1008--1017},
  year={2021}
}

And this is the result I am obtaining

and here is the model1-num-names.bst file : https://docdro.id/8l8VL89

Answer 1

The posted code does not produce the output shown, it makes

with et al not used.

If you repeat the paragraph you get

With et al used consistently for repeat citations. This is a deliberate design decision by the publisher to give full information in a first citation and a compressed form later.

You could use a different bibliography style, but the journal publisher may not accept it, the point of using a journal template like this is that the publisher makes the design decisions.