Issue with untitled references in Sanity schema resolved with upgrade to v2.1.6

export default {
    title: 'Versprechen Page',
    name: 'promise',
    type: 'document',
    ...
    fields: [
        {
            name: 'section1',
            type: 'section',
            fieldset: 'sectionGroup0'
        },
        ... ]
}

export default {
    title: 'Abschnitt',
    name: 'section',
    type: 'document',
    fields: [
        ...
        {
            title: 'Content',
            name: 'content',
            type: 'array',
            of: [
                {
                    type: 'reference',
                    to: [
                        {type: 'pictureAndText'},
                        {type: 'titleAndText'},
                        {type: 'collection'},
                        {type: 'link'}
                    ]
                }
            ]
        },
       ...
    ],
}

preview: {
  select: {
    title: "myFieldToUse"
  },
},

export default{
    title: 'Titel und Text',
    name: 'titleAndText',
    type: 'document',
    fields: [
        {
            title: 'Title',
            name: 'title',
            type: 'string'
        },
        {
            title: 'Text',
            name: 'text',
            type: 'array',
            of:[
                {type:'block'}
            ]
        },
        {
            title: 'Custom Type',
            name: 'custom',
            type: 'string'
        },
    ],
    preview: {
        select: {
            title: 'title',
        },
        prepare(selection) {
            const {title} = selection
            return {
                title: title,
            }
        },
    }
}

to: [
  {
    type: 'pictureAndText'
    preview: {
      title: title
    }
  },
]

"@sanity/base": "2.1.4",