Editing pages in New Editor (Fabric) return "Something went wrong while loading the editor" error

Issue Summary

When editing pages in the new editor, an error stating "Something went wrong while loading the editor" is presented, causing the editing experience to fail. This was mainly observed after converting pages from the Legacy Editor into the New Editor

This is reproducible on Data Center: (no)

Steps to Reproduce

1. Create a page in the Legacy editor
2. Add tasks within a bullet list
3. Publish the page
4. Edit and convert the page to the new editor
5. Edit page

Expected Results

Editor loads and content can be edited

Actual Results

A pop-up error with "Something went wrong while loading the editor" is shown. In the browser network tab, the error below is returned:

error: "Failed to send Content Reset request to Collab Service!. Response body: Optional[{\"code\":\"PROSEMIRROR_SCHEMA_VALIDATION_ERROR\",\"message\":\"ADF document could not be converted to ProseMirror node\",\"meta\":\"Invalid content for node listItem: <taskList(taskItem(text_node), taskItem(text_node)\",\"status\":400}]" 

In the actual page content, you will find the broken content indicated by the following information box:

Workaround

Please contact the Atlassian support team and reference this bug report.