Block-fields with text break within an structure

Hello,
after two long nights without a solution I ask this.
I have a blocks field in a structure field. If I use a markdown- or textfield for a block, the saved json is broken/ invalid. I read about the “pretty: false” option and I switched it off.
Any ideas?
I use Kirby 3.8

THX

Where does the error occur? In the frond-end? In the Panel? Have you already tested this with an up-to-date Starterkit? If this was an issue in older versions, it might already have been fixed,.

Also, please post the blueprint definition for your structure field and if any content in the markdown block causes the issue or only specific content.

Given the information you provided, I cannot reproduce the issue in 3.9.6.1.

This information is not useful, I need something to throw at a Starterkit to test.

What I did test without issues:

title: Test

fields:
  structure:
    type: structure
    fields:
      block:
        type: blocks

Sorry, I edited my post and sent it too early

The error occurs in the resulting textfile. So in the front-end my structure ist not readable.

I didnt test it in a clean starterkit. I will try later.

The error occurs in any content. I tested texts with/without umlauts and special chars.

groups/theblocks.yml

type: blocks
  
fieldsets:
  texte:
    label: Text
    type: group
    fieldsets:              

       markdown:      
        extends: blocks/markdown
        preview: fields 
        wysiwyg: true 
        label: "{{ text }}"
        name: Text
        icon: text
        fields:                                          
          colors: fields/colorandbackground

...

page.yml

t_global_texts:

    sections:
      texts:
        type: fields
        fields:           
          global_texts:
            label: Globale Textblöcke
            type: structure 
            duplicate: false
            translate: false
            sortBy: short aesc
            fields:
              autoid:
                type: hidden  
                translate: false
              short:
                type: text
              h_de: 
                extends: fields/heading
              de:
                extends: fields/markdowneditor      
                label: Text DE
              blocks_de: 
                extends: groups/theblocks
                label: Blöcke DE

...

the de-textfield works fine. Any textfield as a block don’t work.
THX, André