Discarding a shared draft for a new page does not allow other users to save or discard the changes in the page afterwards

Summary

Scenario

Two users are editing a newly created page, whereby user A created the page and passed the URL <base-url>/pages/resumedraft.action?draftId=xxxxx&draftShareId=xxxxx to user B.

Outcome #1

If user A closes the editor (as the creator of the page draft), user B will not be able to publish the changes or close the editor.

Outcome #2

If user B closes the editor, the user gets an error in the top-right corner of the editor that says, "There were errors discarding your draft. An unknown error has occurred. Please check your logs."

Steps to reproduce

1. Login as user A in a browser and login as user B in incognito browser.
2. As user A, create a new page.
3. Copy paste the link in incognito browser so user B can join the editing session.
4. Add some text.

For outcome #1

1. Get user A to click on 'Close' and 'Discard everyone's changes'.
2. Afterwards, get user B to try to publish the page.

For outcome #2:

1. Get user B to click on 'Close' and 'Discard everyone's changes'.

Expected Results

For both outcome #1 and #2, the page should be able to be discarded or saved depending on the user's option.

Actual Results

For outcome #1:

The page just loads, but nothing happens. This is what we see in the browser console:

For outcome #2:

We see the following error in the editor: