CodeSandbox.io has been freezing on Embed mode.

🐛 bug report

Preflight Checklist

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

Description of the problem

These days, we are reviewing the CodeSandbox.io as an main source code sharing platform for Korea Developers.
And we are really satisfying the feature comparing other competitors.

However, during testing the code sharing feature that you provided using embedding iframe code,
we’ve faced the issue that whole web browser has been freezing and shut down when it comes to click the “rdlx-json” file that we’ve created for our products.

We are using “Static” html templated and it works fine showing the results through CodeSandbox.io, but source code tabs for “rdlx-json”.

• https://codesandbox.io/s/arjs-invoice-sample-kr-6mgt8

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

codesandbox editor has been freezing ... and browsers too.
so I could not share the code with customers through Codesandbox.

To Reproduce

You could easily reproduce this issue using attached HTML Sample code.
If you click the code tabs, codesandbox editor has been freezing ... and browsers too.

ARJS-CodeSandBox-Embed-Test.zip

Link to sandbox: link (optional)

https://codesandbox.io/s/arjs-invoice-sample-kr-6mgt8

Your Environment

Start by reproducing the freeze in the linked CodeSandbox embed using the provided ARJS-CodeSandBox-Embed-Test.zip, opening the rdlx-json tab in Chrome on Windows 10. Trace the embed/editor path involved in loading that tab; done means the embedded editor and browser remain responsive when it is opened.