[BUG] The .mjs file execute twice in VanillaJS template

[bcjohnblue]

🐛 bug report

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• [x] I have read the Contributing Guidelines for this project.
• [x] I agree to follow the Code of Conduct that this project adheres to.
• [x] I have searched the issue tracker for an issue that matches the one I want to file, without success.

Description of the problem

In some situation, the .mjs file will execute twice in VanillaJS template.

How has this issue affected you? What are you trying to accomplish?

All of the code in .mjs file would be executed twice and it's weird.

To Reproduce

Link to sandbox: [BUG] .mjs file execute twice (optional)

Your Environment

Software	Name/Version
Сodesandbox	See the link above
Browser	Chrome 114
Operating System	Mac