I'm working with ejs files, but in order to reuse some code, I'm using the includes feature. Given that some opening/closing html tags are placed in other files, after I save my changes, something (I don't know if prettier extension or VS code editor) is including the closing tags into my code, causing several problems when I running it.
I don't use EJS myself, but after playing around with it in VSCode, I noticed that my .ejs files were being treated as HTML files. You can see how your VSCode is interpreting the file by looking in the bottom right corner of the editor. You could search for EJS extensions as well.
You likely have the "Editor: format on save" option enabled. To disable that setting, go to Preferences, and in the search bar type "format on save". Find the setting. Uncheck the box. That should fix the problem.
If, as you mentioned, your closing HTML tags are in other files, then you have invalid HTML and the formatter (both Prettier's and the default one) will autocomplete the closing tag. (I would wager EJS also wouldn't like the lack of closing tags, but since I don't use it I'm not so sure, maybe it's fine.)