Problems with Email Editor after Version 4 upgrade

Your software
My PHP version is : 7.4.25

Updating/Installing Errors
I am (delete as applicable): Updating

My problem is :
I have 3 problems:

  1. After upgrading, every time I clone an email I created before the update, it adds a nullnull string at the beginning of the email.

  2. I can edit and save the email, but when I try to open it again, the email editor does not open, but shows the following screen instead:

  3. On any email that I open the code editor does not open up, so I cannot create a new template email for me to use.

Anybody has an idea what is happening and what I can do to fix that?

Add <!DOCTYPE> To the first line of your email template directly in the db to your emails.custom_html table.
It will work.

I assume it is <!doctype html>
And does it go into the emails table into the custom_html field?
Doing that, I really got my old emails to duplicate and work correctly.

Now I still have a problem with the code editor. Most of the time it still does not open up. What can I do to fix that?

Reload. It will open the second time.
As far as I know 4.0.2 will fix both issues.