Beta: fix minor JS errors

[samiff]

Changes proposed in this Pull Request:

After PR: #20168

There were a few element not found errors since the plugin layout was adjusted; this PR cleans those errors up.

Does this pull request change what data or activity we track or use?

• No.

Testing instructions:

• After pulling down changes, the Beta plugin should function as expected still - try the different plugin sections while you have your browser console open.

[github-actions]

Thank you for your PR!

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Beta plugin:

• Next scheduled release: August 3, 2021.
• Scheduled code freeze: July 26, 2021.