E-Mail Misformed

Your software
My Mautic version is: 4.4.4
My PHP version is: 7.4.29
My Database type and version is: 10.2.44-MariaDB

Your problem
My problem is: The e-mails send to some clients are malformed. Herewith is a screenshot.

This also happened when Mautic 4.0 came out. So we reverted to Mautic 3. This year we decided to give Mautic 4 another chance since there have been several updates. We installed a cleaned version of Mautic 4 and imported the database. We have been sending a few e-mails until yesterday when a client responded to our e-mail and we saw the malformed e-mail. In the past where the e-mails were malformed, we used the Blank template. We have now used Brienz. The GrapesJS plugin is installed.

These errors are showing in the log: None

Steps I have tried to fix the problem: Switched from Blank template to Brienze template

Hi, it seems, you are deleting some sections and columns there.
Here is a video about how the email builder works.
From min. 6:00 Im explaining the sections and columns