Fields are saved, but not loaded for some blocks

Question

I'm experiencing an issue on my development-environment, and I cannot figure out what's going on.

It seems that the fields of some of our blocks aren't being retrieved after saving. To reproduce I create a new entry, add one of the broken blocks, fill in the fields and save. Now when I reopen the entry, most fields are empty again.

Searching for the strings in the database does show that they are being saved under 'matrixcontent_page_blocks.field_modulename_fieldname', but for some reason they're not being retrieved when loading.

other info:

• We're adding all of our custom modules to 2 matrix fields 'generic_blocks' and 'page_blocks' which we use to set the allowed modules for specific entry types (some entry-types contain page_blocks, some generic_blocks)
• The fields that aren't saved are of type: `craft\fields\PlainText
• I've added an example of one of the configs that isn't working, to be clear it's the textfields slogan, label_headline_title and label_headline_sub_title that aren't functional:

field: 17ab0f71-9fbc-4026-a17c-4898662c7469 # Page blocks
fieldLayouts:
  eb83dd13-222b-4106-8f22-2fe1ac8e70bb:
    tabs:
      -
        elements:
          -
            fieldUid: 8c98bc7a-8f92-4033-b19f-7607b4d0903a # Slogan
            instructions: null
            label: null
            required: false
            tip: null
            type: craft\fieldlayoutelements\CustomField
            warning: null
            width: 100
          -
            fieldUid: f51f21ab-e9e7-49a7-b70a-daf96d2d9ebe # Label headline title
            instructions: null
            label: null
            required: false
            tip: null
            type: craft\fieldlayoutelements\CustomField
            warning: null
            width: 100
          -
            fieldUid: 2ff8f89a-c700-4f37-a9e7-a7f63db590c5 # Images
            instructions: null
            label: null
            required: false
            tip: null
            type: craft\fieldlayoutelements\CustomField
            warning: null
            width: 100
          -
            fieldUid: 27a71ff6-d5ab-42f3-8e3f-f6087371f32b # Label headline sub title
            instructions: null
            label: null
            required: false
            tip: null
            type: craft\fieldlayoutelements\CustomField
            warning: null
            width: 100
        name: Content
        sortOrder: 1
fields:
  2ff8f89a-c700-4f37-a9e7-a7f63db590c5: # Images
    columnSuffix: null
    contentColumnType: string
    fieldGroup: null
    handle: images
    instructions: ''
    name: Images
    searchable: true
    settings:
      columns:
        __assoc__:
          -
            - 8f765383-4849-46b1-8b8e-ba731f8c3abe # Image (1818x992)
            -
              __assoc__:
                -
                  - width
                  - ''
          -
            - 5d5eecac-ed41-42bf-9287-75ff80dff968 # Image Title
            -
              __assoc__:
                -
                  - width
                  - ''
      contentTable: '{{%stc_21_images}}'
      fieldLayout: matrix
      maxRows: '10'
      minRows: ''
      placeholderKey: null
      propagationMethod: all
      selectionLabel: ''
      staticField: ''
    translationKeyFormat: null
    translationMethod: site
    type: verbb\supertable\fields\SuperTableField
  8c98bc7a-8f92-4033-b19f-7607b4d0903a: # Slogan
    columnSuffix: null
    contentColumnType: text
    fieldGroup: null
    handle: slogan
    instructions: ''
    name: Slogan
    searchable: true
    settings:
      byteLimit: null
      charLimit: null
      code: ''
      columnType: null
      initialRows: '4'
      multiline: ''
      placeholder: null
      uiMode: normal
    translationKeyFormat: null
    translationMethod: language
    type: craft\fields\PlainText
  27a71ff6-d5ab-42f3-8e3f-f6087371f32b: # Label headline sub title
    columnSuffix: null
    contentColumnType: text
    fieldGroup: null
    handle: label_headline_sub_title
    instructions: 'Recommended max 50 characters'
    name: 'Label headline sub title'
    searchable: true
    settings:
      byteLimit: null
      charLimit: null
      code: ''
      columnType: null
      initialRows: '4'
      multiline: ''
      placeholder: null
      uiMode: normal
    translationKeyFormat: null
    translationMethod: language
    type: craft\fields\PlainText
  f51f21ab-e9e7-49a7-b70a-daf96d2d9ebe: # Label headline title
    columnSuffix: null
    contentColumnType: text
    fieldGroup: null
    handle: label_headline_title
    instructions: 'Recommended max 40 characters'
    name: 'Label headline title'
    searchable: true
    settings:
      byteLimit: null
      charLimit: null
      code: ''
      columnType: null
      initialRows: '4'
      multiline: ''
      placeholder: null
      uiMode: normal
    translationKeyFormat: null
    translationMethod: language
    type: craft\fields\PlainText
handle: module_carousel
name: Carousel
sortOrder: 5