Steps to reproduce:

• Add a custom style and tag...for example:

  ezpublish:
      system:
          admin_group:
              fieldtypes:
                  ezrichtext:
                      custom_tags:
                          - variable_fontsize
                      custom_styles:
                          - color_black
  
  ezrichtext:
      custom_tags:
          variable_fontsize:
              template: 'field_type/ezrichtext/custom_tag/custom-fontsize.html.twig'
              icon: '/bundles/ezplatformadminui/img/ez-icons.svg#content-type'
              is_inline: true
              attributes:
                  font_size:
                      type: number
                      required: true
      custom_styles:
          color_black:
              template: 'field_type/ezrichtext/custom_style/inline-color.html.twig'
              inline: true
  

• Edit a richtext field and add the custom style to a random word and include the custom tag somewhere inside the same paragraph
• Remove the custom style by clicking on "normal"
• Richtextfield should break