The existing page layout breaks while trying to add a new page layout

Issue Summary

On a complex layout applied page, the existing page layout breaks and becomes unusable when trying to add a new page layout. Please see the screen recording below:
screenrecording.mp4

This is reproducible on Data Center: yes

Steps to Reproduce

1. Please use the following storage format to create the example page: anonimized-storageformat.txt
2. After the page is created, please go the Edit mode again and click the "Page layout" icon on top of the editor

Expected Results

A new page layout is added without any issues.

Actual Results

The existing page layout breaks and is distorted, the page becomes unusable.

Workaround

Currently there is no known workaround for this behavior. A workaround will be added here when available