Troubleshooting a schema issue with reference fields in Slack thread

Reference search failed
Attribute name cannot be an empty string

<https://x6q9abew.api.sanity.io/v2021-03-25/data/query/development?query=*[_type> in $__types&&!(_id in path('drafts.**'))][0...$__limit]{_type == "pageArchive" => { "w0": _id,"w1": _type,"w2": title,"w3": @[""],"w4": slug.current,"w5": message,"w6": seo.seoTitle,"w7": seo.seoDescription },}&$__types=["pageArchive"]&$__limit=1000&tag=sanity.studio.search.reference

@sanity/cli                  2.1.4 (latest: 2.18.0)
@sanity/base                2.17.0 (latest: 2.18.0)
@sanity/cli                 2.17.0 (latest: 2.18.0)
@sanity/components          2.14.0 (up to date)
@sanity/core                2.17.0 (latest: 2.18.0)
@sanity/dashboard           2.17.0 (latest: 2.18.0)
@sanity/default-layout      2.17.0 (latest: 2.18.0)
@sanity/default-login       2.17.0 (latest: 2.18.0)
@sanity/desk-tool           2.17.0 (latest: 2.18.0)
@sanity/production-preview  2.15.0 (up to date)
@sanity/uuid                 3.0.1 (up to date)
@sanity/vision              2.15.0 (latest: 2.17.2)

{
    "name": "pageArchive",
    "title": "Archive Page",
    "type": "document",
    "__experimental_actions": ["update", "publish"],
    "fieldsets": [
        {
            "name": "seo",
            "title": "SEO",
            "options": {
                "collapsible": true,
                "collapsed": true
            }
        },
        {
            "name": "meta",
            "title": "Meta",
            "options": {
                "collapsible": true,
                "collapsed": true
            }
        }
    ],
    "fields": [
        {
            "name": "title",
            "title": "Title",
            "validation": null,
            "type": "string"
        },
        {
            "name": "slug",
            "title": "Slug",
            "description": "Leave blank to autofill.",
            "options": {
                "source": "title",
                "maxLength": 96,
                "minLength": 4
            },
            "readOnly": true,
            "type": "slug",
            "fieldset": "meta"
        },
        {
            "name": "message",
            "title": "Message",
            "validation": null,
            "message": "This page is populated with Posts",
            "inputComponent": {
                "propTypes": {}
            },
            "type": "string"
        },
        {
            "name": "seo",
            "title": " ",
            "validation": null,
            "fieldset": "seo",
            "type": "seo"
        }
    ],
    "preview": {
        "select": {
            "title": "title",
            "media": "image",
            "subtitle": ""
        }
    }
}