Expand Source button in Code Block macro sometimes doesn't appear in the Legacy Editor

Issue Summary

The Code Block macro can be configured to be collapsible when in the Legacy Editor. However, sometimes the expand source button doesn't show up and users are unable to see the content in the macro.

Steps to Reproduce

1. Create a page using the Legacy template
2. Add the Code Block macro.
3. Make it collapsible.
4. Access the page several times until the expand source button will stop showing up.

Expected Results

The expand source button should appear.

Actual Results

The expand source button doesn't appear.

Workaround

Users can convert the pages to the new editor and put the code block inside the Expand macro.