Steps to reproduce:

1. Create the following custom blocks configuration:

   ezplatform_page_fieldtype:
       blocks:
           text_block:
               name: Example Block
               category: default
               thumbnail: assets/images/blocks/exampleblock.svg
               configuration_template: blocks/config.html.twig
               views:
                   default:
                       template: blocks/template.html.twig
                       name: Default view
                       priority: -255
               attributes:
                   name:
                       type: text
                       validators:
                           not_blank:
                               message: Please provide a name
           youtube_video:
               name: Example Block
               category: default
               thumbnail: assets/images/blocks/exampleblock.svg
               configuration_template: blocks/config.html.twig
               views:
                   default:
                       template: blocks/template.html.twig
                       name: Default view
                       priority: -255
               attributes:
                   name:
                       type: text
                       validators:
                           not_blank:
                               message: Please provide a name
           article_text_block:
               name: Example Block
               category: default
               thumbnail: assets/images/blocks/exampleblock.svg
               configuration_template: blocks/config.html.twig
               views:
                   default:
                       template: blocks/template.html.twig
                       name: Default view
                       priority: -255
               attributes:
                   name:
                       type: text
                       validators:
                           not_blank:
                               message: Please provide a name
           article_youtube_video:
               name: Example Block
               category: default
               thumbnail: assets/images/blocks/exampleblock.svg
               configuration_template: blocks/config.html.twig
               views:
                   default:
                       template: blocks/template.html.twig
                       name: Default view
                       priority: -255
               attributes:
                   name:
                       type: text
                       validators:
                           not_blank:
                               message: Please provide a name
   

2. Edit LandingPage Content Type => ezlandingpage fieldtype.
3. Use "Select blocks" option.

Result:
Only a single block out of 4 is visible. They are not rendered in the Page Builder as well.

Expected result:
All 4 blocks should be visible both in Content Type form and Page Builder.