SyntaxError: Unexpected token '<', "<!DOCTYPE "... is not valid JSON

{
  "manifest": {
    "error": "SyntaxError: Unexpected token '<', \"<!DOCTYPE \"... is not valid JSON",
    "id": "https://iiif-collection.lib.uchicago.edu/object/ark:61001/b2s81tv2344w.json",
    "isFetching": false
  },
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    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-2208dfd9-22c0-49b3-bf4a-df6ca366439b",
    "manifestId": "https://iiif-collection.lib.uchicago.edu/object/ark:61001/b2s81tv2344w.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-1c9a161b-e615-419c-a616-5146b4695f70",
    "loadedManifest": "https://iiif-collection.lib.uchicago.edu/object/ark:61001/b2s81tv2344w.json",
    "canvasIndex": 2,
    "allowMaximize": false
  }
}